1 Table of contents 2 ----------------- 3 4 1. Overview 5 2. How fio works 6 3. Running fio 7 4. Job file format 8 5. Detailed list of parameters 9 6. Normal output 10 7. Terse output 11 8. Trace file format 12 9. CPU idleness profiling 13 14 1.0 Overview and history 15 ------------------------ 16 fio was originally written to save me the hassle of writing special test 17 case programs when I wanted to test a specific workload, either for 18 performance reasons or to find/reproduce a bug. The process of writing 19 such a test app can be tiresome, especially if you have to do it often. 20 Hence I needed a tool that would be able to simulate a given io workload 21 without resorting to writing a tailored test case again and again. 22 23 A test work load is difficult to define, though. There can be any number 24 of processes or threads involved, and they can each be using their own 25 way of generating io. You could have someone dirtying large amounts of 26 memory in an memory mapped file, or maybe several threads issuing 27 reads using asynchronous io. fio needed to be flexible enough to 28 simulate both of these cases, and many more. 29 30 2.0 How fio works 31 ----------------- 32 The first step in getting fio to simulate a desired io workload, is 33 writing a job file describing that specific setup. A job file may contain 34 any number of threads and/or files - the typical contents of the job file 35 is a global section defining shared parameters, and one or more job 36 sections describing the jobs involved. When run, fio parses this file 37 and sets everything up as described. If we break down a job from top to 38 bottom, it contains the following basic parameters: 39 40 IO type Defines the io pattern issued to the file(s). 41 We may only be reading sequentially from this 42 file(s), or we may be writing randomly. Or even 43 mixing reads and writes, sequentially or randomly. 44 45 Block size In how large chunks are we issuing io? This may be 46 a single value, or it may describe a range of 47 block sizes. 48 49 IO size How much data are we going to be reading/writing. 50 51 IO engine How do we issue io? We could be memory mapping the 52 file, we could be using regular read/write, we 53 could be using splice, async io, syslet, or even 54 SG (SCSI generic sg). 55 56 IO depth If the io engine is async, how large a queuing 57 depth do we want to maintain? 58 59 IO type Should we be doing buffered io, or direct/raw io? 60 61 Num files How many files are we spreading the workload over. 62 63 Num threads How many threads or processes should we spread 64 this workload over. 65 66 The above are the basic parameters defined for a workload, in addition 67 there's a multitude of parameters that modify other aspects of how this 68 job behaves. 69 70 71 3.0 Running fio 72 --------------- 73 See the README file for command line parameters, there are only a few 74 of them. 75 76 Running fio is normally the easiest part - you just give it the job file 77 (or job files) as parameters: 78 79 $ fio job_file 80 81 and it will start doing what the job_file tells it to do. You can give 82 more than one job file on the command line, fio will serialize the running 83 of those files. Internally that is the same as using the 'stonewall' 84 parameter described the the parameter section. 85 86 If the job file contains only one job, you may as well just give the 87 parameters on the command line. The command line parameters are identical 88 to the job parameters, with a few extra that control global parameters 89 (see README). For example, for the job file parameter iodepth=2, the 90 mirror command line option would be --iodepth 2 or --iodepth=2. You can 91 also use the command line for giving more than one job entry. For each 92 --name option that fio sees, it will start a new job with that name. 93 Command line entries following a --name entry will apply to that job, 94 until there are no more entries or a new --name entry is seen. This is 95 similar to the job file options, where each option applies to the current 96 job until a new [] job entry is seen. 97 98 fio does not need to run as root, except if the files or devices specified 99 in the job section requires that. Some other options may also be restricted, 100 such as memory locking, io scheduler switching, and decreasing the nice value. 101 102 103 4.0 Job file format 104 ------------------- 105 As previously described, fio accepts one or more job files describing 106 what it is supposed to do. The job file format is the classic ini file, 107 where the names enclosed in [] brackets define the job name. You are free 108 to use any ascii name you want, except 'global' which has special meaning. 109 A global section sets defaults for the jobs described in that file. A job 110 may override a global section parameter, and a job file may even have 111 several global sections if so desired. A job is only affected by a global 112 section residing above it. If the first character in a line is a ';' or a 113 '#', the entire line is discarded as a comment. 114 115 So let's look at a really simple job file that defines two processes, each 116 randomly reading from a 128MB file. 117 118 ; -- start job file -- 119 [global] 120 rw=randread 121 size=128m 122 123 [job1] 124 125 [job2] 126 127 ; -- end job file -- 128 129 As you can see, the job file sections themselves are empty as all the 130 described parameters are shared. As no filename= option is given, fio 131 makes up a filename for each of the jobs as it sees fit. On the command 132 line, this job would look as follows: 133 134 $ fio --name=global --rw=randread --size=128m --name=job1 --name=job2 135 136 137 Let's look at an example that has a number of processes writing randomly 138 to files. 139 140 ; -- start job file -- 141 [random-writers] 142 ioengine=libaio 143 iodepth=4 144 rw=randwrite 145 bs=32k 146 direct=0 147 size=64m 148 numjobs=4 149 150 ; -- end job file -- 151 152 Here we have no global section, as we only have one job defined anyway. 153 We want to use async io here, with a depth of 4 for each file. We also 154 increased the buffer size used to 32KB and define numjobs to 4 to 155 fork 4 identical jobs. The result is 4 processes each randomly writing 156 to their own 64MB file. Instead of using the above job file, you could 157 have given the parameters on the command line. For this case, you would 158 specify: 159 160 $ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4 161 162 4.1 Environment variables 163 ------------------------- 164 165 fio also supports environment variable expansion in job files. Any 166 substring of the form "${VARNAME}" as part of an option value (in other 167 words, on the right of the `='), will be expanded to the value of the 168 environment variable called VARNAME. If no such environment variable 169 is defined, or VARNAME is the empty string, the empty string will be 170 substituted. 171 172 As an example, let's look at a sample fio invocation and job file: 173 174 $ SIZE=64m NUMJOBS=4 fio jobfile.fio 175 176 ; -- start job file -- 177 [random-writers] 178 rw=randwrite 179 size=${SIZE} 180 numjobs=${NUMJOBS} 181 ; -- end job file -- 182 183 This will expand to the following equivalent job file at runtime: 184 185 ; -- start job file -- 186 [random-writers] 187 rw=randwrite 188 size=64m 189 numjobs=4 190 ; -- end job file -- 191 192 fio ships with a few example job files, you can also look there for 193 inspiration. 194 195 4.2 Reserved keywords 196 --------------------- 197 198 Additionally, fio has a set of reserved keywords that will be replaced 199 internally with the appropriate value. Those keywords are: 200 201 $pagesize The architecture page size of the running system 202 $mb_memory Megabytes of total memory in the system 203 $ncpus Number of online available CPUs 204 205 These can be used on the command line or in the job file, and will be 206 automatically substituted with the current system values when the job 207 is run. Simple math is also supported on these keywords, so you can 208 perform actions like: 209 210 size=8*$mb_memory 211 212 and get that properly expanded to 8 times the size of memory in the 213 machine. 214 215 216 5.0 Detailed list of parameters 217 ------------------------------- 218 219 This section describes in details each parameter associated with a job. 220 Some parameters take an option of a given type, such as an integer or 221 a string. The following types are used: 222 223 str String. This is a sequence of alpha characters. 224 time Integer with possible time suffix. In seconds unless otherwise 225 specified, use eg 10m for 10 minutes. Accepts s/m/h for seconds, 226 minutes, and hours, and accepts 'ms' (or 'msec') for milliseconds, 227 and 'us' (or 'usec') for microseconds. 228 int SI integer. A whole number value, which may contain a suffix 229 describing the base of the number. Accepted suffixes are k/m/g/t/p, 230 meaning kilo, mega, giga, tera, and peta. The suffix is not case 231 sensitive, and you may also include trailing 'b' (eg 'kb' is the same 232 as 'k'). So if you want to specify 4096, you could either write 233 out '4096' or just give 4k. The suffixes signify base 2 values, so 234 1024 is 1k and 1024k is 1m and so on, unless the suffix is explicitly 235 set to a base 10 value using 'kib', 'mib', 'gib', etc. If that is the 236 case, then 1000 is used as the multiplier. This can be handy for 237 disks, since manufacturers generally use base 10 values when listing 238 the capacity of a drive. If the option accepts an upper and lower 239 range, use a colon ':' or minus '-' to separate such values. May also 240 include a prefix to indicate numbers base. If 0x is used, the number 241 is assumed to be hexadecimal. See irange. 242 bool Boolean. Usually parsed as an integer, however only defined for 243 true and false (1 and 0). 244 irange Integer range with suffix. Allows value range to be given, such 245 as 1024-4096. A colon may also be used as the separator, eg 246 1k:4k. If the option allows two sets of ranges, they can be 247 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see 248 int. 249 float_list A list of floating numbers, separated by a ':' character. 250 251 With the above in mind, here follows the complete list of fio job 252 parameters. 253 254 name=str ASCII name of the job. This may be used to override the 255 name printed by fio for this job. Otherwise the job 256 name is used. On the command line this parameter has the 257 special purpose of also signaling the start of a new 258 job. 259 260 description=str Text description of the job. Doesn't do anything except 261 dump this text description when this job is run. It's 262 not parsed. 263 264 directory=str Prefix filenames with this directory. Used to place files 265 in a different location than "./". See the 'filename' option 266 for escaping certain characters. 267 268 filename=str Fio normally makes up a filename based on the job name, 269 thread number, and file number. If you want to share 270 files between threads in a job or several jobs, specify 271 a filename for each of them to override the default. If 272 the ioengine used is 'net', the filename is the host, port, 273 and protocol to use in the format of =host,port,protocol. 274 See ioengine=net for more. If the ioengine is file based, you 275 can specify a number of files by separating the names with a 276 ':' colon. So if you wanted a job to open /dev/sda and /dev/sdb 277 as the two working files, you would use 278 filename=/dev/sda:/dev/sdb. On Windows, disk devices are 279 accessed as \\.\PhysicalDrive0 for the first device, 280 \\.\PhysicalDrive1 for the second etc. Note: Windows and 281 FreeBSD prevent write access to areas of the disk containing 282 in-use data (e.g. filesystems). 283 If the wanted filename does need to include a colon, then 284 escape that with a '\' character. For instance, if the filename 285 is "/dev/dsk/foo@3,0:c", then you would use 286 filename="/dev/dsk/foo@3,0\:c". '-' is a reserved name, meaning 287 stdin or stdout. Which of the two depends on the read/write 288 direction set. 289 290 filename_format=str 291 If sharing multiple files between jobs, it is usually necessary 292 to have fio generate the exact names that you want. By default, 293 fio will name a file based on the default file format 294 specification of jobname.jobnumber.filenumber. With this 295 option, that can be customized. Fio will recognize and replace 296 the following keywords in this string: 297 298 $jobname 299 The name of the worker thread or process. 300 301 $jobnum 302 The incremental number of the worker thread or 303 process. 304 305 $filenum 306 The incremental number of the file for that worker 307 thread or process. 308 309 To have dependent jobs share a set of files, this option can 310 be set to have fio generate filenames that are shared between 311 the two. For instance, if testfiles.$filenum is specified, 312 file number 4 for any job will be named testfiles.4. The 313 default of $jobname.$jobnum.$filenum will be used if 314 no other format specifier is given. 315 316 opendir=str Tell fio to recursively add any file it can find in this 317 directory and down the file system tree. 318 319 lockfile=str Fio defaults to not locking any files before it does 320 IO to them. If a file or file descriptor is shared, fio 321 can serialize IO to that file to make the end result 322 consistent. This is usual for emulating real workloads that 323 share files. The lock modes are: 324 325 none No locking. The default. 326 exclusive Only one thread/process may do IO, 327 excluding all others. 328 readwrite Read-write locking on the file. Many 329 readers may access the file at the 330 same time, but writes get exclusive 331 access. 332 333 readwrite=str 334 rw=str Type of io pattern. Accepted values are: 335 336 read Sequential reads 337 write Sequential writes 338 randwrite Random writes 339 randread Random reads 340 rw,readwrite Sequential mixed reads and writes 341 randrw Random mixed reads and writes 342 343 For the mixed io types, the default is to split them 50/50. 344 For certain types of io the result may still be skewed a bit, 345 since the speed may be different. It is possible to specify 346 a number of IO's to do before getting a new offset, this is 347 one by appending a ':<nr>' to the end of the string given. 348 For a random read, it would look like 'rw=randread:8' for 349 passing in an offset modifier with a value of 8. If the 350 suffix is used with a sequential IO pattern, then the value 351 specified will be added to the generated offset for each IO. 352 For instance, using rw=write:4k will skip 4k for every 353 write. It turns sequential IO into sequential IO with holes. 354 See the 'rw_sequencer' option. 355 356 rw_sequencer=str If an offset modifier is given by appending a number to 357 the rw=<str> line, then this option controls how that 358 number modifies the IO offset being generated. Accepted 359 values are: 360 361 sequential Generate sequential offset 362 identical Generate the same offset 363 364 'sequential' is only useful for random IO, where fio would 365 normally generate a new random offset for every IO. If you 366 append eg 8 to randread, you would get a new random offset for 367 every 8 IO's. The result would be a seek for only every 8 368 IO's, instead of for every IO. Use rw=randread:8 to specify 369 that. As sequential IO is already sequential, setting 370 'sequential' for that would not result in any differences. 371 'identical' behaves in a similar fashion, except it sends 372 the same offset 8 number of times before generating a new 373 offset. 374 375 kb_base=int The base unit for a kilobyte. The defacto base is 2^10, 1024. 376 Storage manufacturers like to use 10^3 or 1000 as a base 377 ten unit instead, for obvious reasons. Allow values are 378 1024 or 1000, with 1024 being the default. 379 380 unified_rw_reporting=bool Fio normally reports statistics on a per 381 data direction basis, meaning that read, write, and trim are 382 accounted and reported separately. If this option is set, 383 the fio will sum the results and report them as "mixed" 384 instead. 385 386 randrepeat=bool For random IO workloads, seed the generator in a predictable 387 way so that results are repeatable across repetitions. 388 389 randseed=int Seed the random number generators based on this seed value, to 390 be able to control what sequence of output is being generated. 391 If not set, the random sequence depends on the randrepeat 392 setting. 393 394 use_os_rand=bool Fio can either use the random generator supplied by the OS 395 to generator random offsets, or it can use it's own internal 396 generator (based on Tausworthe). Default is to use the 397 internal generator, which is often of better quality and 398 faster. 399 400 fallocate=str Whether pre-allocation is performed when laying down files. 401 Accepted values are: 402 403 none Do not pre-allocate space 404 posix Pre-allocate via posix_fallocate() 405 keep Pre-allocate via fallocate() with 406 FALLOC_FL_KEEP_SIZE set 407 0 Backward-compatible alias for 'none' 408 1 Backward-compatible alias for 'posix' 409 410 May not be available on all supported platforms. 'keep' is only 411 available on Linux.If using ZFS on Solaris this must be set to 412 'none' because ZFS doesn't support it. Default: 'posix'. 413 414 fadvise_hint=bool By default, fio will use fadvise() to advise the kernel 415 on what IO patterns it is likely to issue. Sometimes you 416 want to test specific IO patterns without telling the 417 kernel about it, in which case you can disable this option. 418 If set, fio will use POSIX_FADV_SEQUENTIAL for sequential 419 IO and POSIX_FADV_RANDOM for random IO. 420 421 size=int The total size of file io for this job. Fio will run until 422 this many bytes has been transferred, unless runtime is 423 limited by other options (such as 'runtime', for instance). 424 Unless specific nrfiles and filesize options are given, 425 fio will divide this size between the available files 426 specified by the job. If not set, fio will use the full 427 size of the given files or devices. If the the files 428 do not exist, size must be given. It is also possible to 429 give size as a percentage between 1 and 100. If size=20% 430 is given, fio will use 20% of the full size of the given 431 files or devices. 432 433 io_limit=int Normally fio operates within the region set by 'size', which 434 means that the 'size' option sets both the region and size of 435 IO to be performed. Sometimes that is not what you want. With 436 this option, it is possible to define just the amount of IO 437 that fio should do. For instance, if 'size' is set to 20G and 438 'io_limit' is set to 5G, fio will perform IO within the first 439 20G but exit when 5G have been done. 440 441 filesize=int Individual file sizes. May be a range, in which case fio 442 will select sizes for files at random within the given range 443 and limited to 'size' in total (if that is given). If not 444 given, each created file is the same size. 445 446 file_append=bool Perform IO after the end of the file. Normally fio will 447 operate within the size of a file. If this option is set, then 448 fio will append to the file instead. This has identical 449 behavior to setting offset to the size of a file. This option 450 is ignored on non-regular files. 451 452 fill_device=bool 453 fill_fs=bool Sets size to something really large and waits for ENOSPC (no 454 space left on device) as the terminating condition. Only makes 455 sense with sequential write. For a read workload, the mount 456 point will be filled first then IO started on the result. This 457 option doesn't make sense if operating on a raw device node, 458 since the size of that is already known by the file system. 459 Additionally, writing beyond end-of-device will not return 460 ENOSPC there. 461 462 blocksize=int 463 bs=int The block size used for the io units. Defaults to 4k. Values 464 can be given for both read and writes. If a single int is 465 given, it will apply to both. If a second int is specified 466 after a comma, it will apply to writes only. In other words, 467 the format is either bs=read_and_write or bs=read,write,trim. 468 bs=4k,8k will thus use 4k blocks for reads, 8k blocks for 469 writes, and 8k for trims. You can terminate the list with 470 a trailing comma. bs=4k,8k, would use the default value for 471 trims.. If you only wish to set the write size, you 472 can do so by passing an empty read size - bs=,8k will set 473 8k for writes and leave the read default value. 474 475 blockalign=int 476 ba=int At what boundary to align random IO offsets. Defaults to 477 the same as 'blocksize' the minimum blocksize given. 478 Minimum alignment is typically 512b for using direct IO, 479 though it usually depends on the hardware block size. This 480 option is mutually exclusive with using a random map for 481 files, so it will turn off that option. 482 483 blocksize_range=irange 484 bsrange=irange Instead of giving a single block size, specify a range 485 and fio will mix the issued io block sizes. The issued 486 io unit will always be a multiple of the minimum value 487 given (also see bs_unaligned). Applies to both reads and 488 writes, however a second range can be given after a comma. 489 See bs=. 490 491 bssplit=str Sometimes you want even finer grained control of the 492 block sizes issued, not just an even split between them. 493 This option allows you to weight various block sizes, 494 so that you are able to define a specific amount of 495 block sizes issued. The format for this option is: 496 497 bssplit=blocksize/percentage:blocksize/percentage 498 499 for as many block sizes as needed. So if you want to define 500 a workload that has 50% 64k blocks, 10% 4k blocks, and 501 40% 32k blocks, you would write: 502 503 bssplit=4k/10:64k/50:32k/40 504 505 Ordering does not matter. If the percentage is left blank, 506 fio will fill in the remaining values evenly. So a bssplit 507 option like this one: 508 509 bssplit=4k/50:1k/:32k/ 510 511 would have 50% 4k ios, and 25% 1k and 32k ios. The percentages 512 always add up to 100, if bssplit is given a range that adds 513 up to more, it will error out. 514 515 bssplit also supports giving separate splits to reads and 516 writes. The format is identical to what bs= accepts. You 517 have to separate the read and write parts with a comma. So 518 if you want a workload that has 50% 2k reads and 50% 4k reads, 519 while having 90% 4k writes and 10% 8k writes, you would 520 specify: 521 522 bssplit=2k/50:4k/50,4k/90,8k/10 523 524 blocksize_unaligned 525 bs_unaligned If this option is given, any byte size value within bsrange 526 may be used as a block range. This typically wont work with 527 direct IO, as that normally requires sector alignment. 528 529 bs_is_seq_rand If this option is set, fio will use the normal read,write 530 blocksize settings as sequential,random instead. Any random 531 read or write will use the WRITE blocksize settings, and any 532 sequential read or write will use the READ blocksize setting. 533 534 zero_buffers If this option is given, fio will init the IO buffers to 535 all zeroes. The default is to fill them with random data. 536 The resulting IO buffers will not be completely zeroed, 537 unless scramble_buffers is also turned off. 538 539 refill_buffers If this option is given, fio will refill the IO buffers 540 on every submit. The default is to only fill it at init 541 time and reuse that data. Only makes sense if zero_buffers 542 isn't specified, naturally. If data verification is enabled, 543 refill_buffers is also automatically enabled. 544 545 scramble_buffers=bool If refill_buffers is too costly and the target is 546 using data deduplication, then setting this option will 547 slightly modify the IO buffer contents to defeat normal 548 de-dupe attempts. This is not enough to defeat more clever 549 block compression attempts, but it will stop naive dedupe of 550 blocks. Default: true. 551 552 buffer_compress_percentage=int If this is set, then fio will attempt to 553 provide IO buffer content (on WRITEs) that compress to 554 the specified level. Fio does this by providing a mix of 555 random data and zeroes. Note that this is per block size 556 unit, for file/disk wide compression level that matches 557 this setting, you'll also want to set refill_buffers. 558 559 buffer_compress_chunk=int See buffer_compress_percentage. This 560 setting allows fio to manage how big the ranges of random 561 data and zeroed data is. Without this set, fio will 562 provide buffer_compress_percentage of blocksize random 563 data, followed by the remaining zeroed. With this set 564 to some chunk size smaller than the block size, fio can 565 alternate random and zeroed data throughout the IO 566 buffer. 567 568 buffer_pattern=str If set, fio will fill the io buffers with this pattern. 569 If not set, the contents of io buffers is defined by the other 570 options related to buffer contents. The setting can be any 571 pattern of bytes, and can be prefixed with 0x for hex values. 572 573 nrfiles=int Number of files to use for this job. Defaults to 1. 574 575 openfiles=int Number of files to keep open at the same time. Defaults to 576 the same as nrfiles, can be set smaller to limit the number 577 simultaneous opens. 578 579 file_service_type=str Defines how fio decides which file from a job to 580 service next. The following types are defined: 581 582 random Just choose a file at random. 583 584 roundrobin Round robin over open files. This 585 is the default. 586 587 sequential Finish one file before moving on to 588 the next. Multiple files can still be 589 open depending on 'openfiles'. 590 591 The string can have a number appended, indicating how 592 often to switch to a new file. So if option random:4 is 593 given, fio will switch to a new random file after 4 ios 594 have been issued. 595 596 ioengine=str Defines how the job issues io to the file. The following 597 types are defined: 598 599 sync Basic read(2) or write(2) io. lseek(2) is 600 used to position the io location. 601 602 psync Basic pread(2) or pwrite(2) io. 603 604 vsync Basic readv(2) or writev(2) IO. 605 606 psyncv Basic preadv(2) or pwritev(2) IO. 607 608 libaio Linux native asynchronous io. Note that Linux 609 may only support queued behaviour with 610 non-buffered IO (set direct=1 or buffered=0). 611 This engine defines engine specific options. 612 613 posixaio glibc posix asynchronous io. 614 615 solarisaio Solaris native asynchronous io. 616 617 windowsaio Windows native asynchronous io. 618 619 mmap File is memory mapped and data copied 620 to/from using memcpy(3). 621 622 splice splice(2) is used to transfer the data and 623 vmsplice(2) to transfer data from user 624 space to the kernel. 625 626 syslet-rw Use the syslet system calls to make 627 regular read/write async. 628 629 sg SCSI generic sg v3 io. May either be 630 synchronous using the SG_IO ioctl, or if 631 the target is an sg character device 632 we use read(2) and write(2) for asynchronous 633 io. 634 635 null Doesn't transfer any data, just pretends 636 to. This is mainly used to exercise fio 637 itself and for debugging/testing purposes. 638 639 net Transfer over the network to given host:port. 640 Depending on the protocol used, the hostname, 641 port, listen and filename options are used to 642 specify what sort of connection to make, while 643 the protocol option determines which protocol 644 will be used. 645 This engine defines engine specific options. 646 647 netsplice Like net, but uses splice/vmsplice to 648 map data and send/receive. 649 This engine defines engine specific options. 650 651 cpuio Doesn't transfer any data, but burns CPU 652 cycles according to the cpuload= and 653 cpucycle= options. Setting cpuload=85 654 will cause that job to do nothing but burn 655 85% of the CPU. In case of SMP machines, 656 use numjobs=<no_of_cpu> to get desired CPU 657 usage, as the cpuload only loads a single 658 CPU at the desired rate. 659 660 guasi The GUASI IO engine is the Generic Userspace 661 Asyncronous Syscall Interface approach 662 to async IO. See 663 664 http://www.xmailserver.org/guasi-lib.html 665 666 for more info on GUASI. 667 668 rdma The RDMA I/O engine supports both RDMA 669 memory semantics (RDMA_WRITE/RDMA_READ) and 670 channel semantics (Send/Recv) for the 671 InfiniBand, RoCE and iWARP protocols. 672 673 falloc IO engine that does regular fallocate to 674 simulate data transfer as fio ioengine. 675 DDIR_READ does fallocate(,mode = keep_size,) 676 DDIR_WRITE does fallocate(,mode = 0) 677 DDIR_TRIM does fallocate(,mode = punch_hole) 678 679 e4defrag IO engine that does regular EXT4_IOC_MOVE_EXT 680 ioctls to simulate defragment activity in 681 request to DDIR_WRITE event 682 683 external Prefix to specify loading an external 684 IO engine object file. Append the engine 685 filename, eg ioengine=external:/tmp/foo.o 686 to load ioengine foo.o in /tmp. 687 688 iodepth=int This defines how many io units to keep in flight against 689 the file. The default is 1 for each file defined in this 690 job, can be overridden with a larger value for higher 691 concurrency. Note that increasing iodepth beyond 1 will not 692 affect synchronous ioengines (except for small degress when 693 verify_async is in use). Even async engines may impose OS 694 restrictions causing the desired depth not to be achieved. 695 This may happen on Linux when using libaio and not setting 696 direct=1, since buffered IO is not async on that OS. Keep an 697 eye on the IO depth distribution in the fio output to verify 698 that the achieved depth is as expected. Default: 1. 699 700 iodepth_batch_submit=int 701 iodepth_batch=int This defines how many pieces of IO to submit at once. 702 It defaults to 1 which means that we submit each IO 703 as soon as it is available, but can be raised to submit 704 bigger batches of IO at the time. 705 706 iodepth_batch_complete=int This defines how many pieces of IO to retrieve 707 at once. It defaults to 1 which means that we'll ask 708 for a minimum of 1 IO in the retrieval process from 709 the kernel. The IO retrieval will go on until we 710 hit the limit set by iodepth_low. If this variable is 711 set to 0, then fio will always check for completed 712 events before queuing more IO. This helps reduce 713 IO latency, at the cost of more retrieval system calls. 714 715 iodepth_low=int The low water mark indicating when to start filling 716 the queue again. Defaults to the same as iodepth, meaning 717 that fio will attempt to keep the queue full at all times. 718 If iodepth is set to eg 16 and iodepth_low is set to 4, then 719 after fio has filled the queue of 16 requests, it will let 720 the depth drain down to 4 before starting to fill it again. 721 722 direct=bool If value is true, use non-buffered io. This is usually 723 O_DIRECT. Note that ZFS on Solaris doesn't support direct io. 724 On Windows the synchronous ioengines don't support direct io. 725 726 atomic=bool If value is true, attempt to use atomic direct IO. Atomic 727 writes are guaranteed to be stable once acknowledged by 728 the operating system. Only Linux supports O_ATOMIC right 729 now. 730 731 buffered=bool If value is true, use buffered io. This is the opposite 732 of the 'direct' option. Defaults to true. 733 734 offset=int Start io at the given offset in the file. The data before 735 the given offset will not be touched. This effectively 736 caps the file size at real_size - offset. 737 738 offset_increment=int If this is provided, then the real offset becomes 739 the offset + offset_increment * thread_number, where the 740 thread number is a counter that starts at 0 and is incremented 741 for each job. This option is useful if there are several jobs 742 which are intended to operate on a file in parallel in disjoint 743 segments, with even spacing between the starting points. 744 745 number_ios=int Fio will normally perform IOs until it has exhausted the size 746 of the region set by size=, or if it exhaust the allocated 747 time (or hits an error condition). With this setting, the 748 range/size can be set independently of the number of IOs to 749 perform. When fio reaches this number, it will exit normally 750 and report status. 751 752 fsync=int If writing to a file, issue a sync of the dirty data 753 for every number of blocks given. For example, if you give 754 32 as a parameter, fio will sync the file for every 32 755 writes issued. If fio is using non-buffered io, we may 756 not sync the file. The exception is the sg io engine, which 757 synchronizes the disk cache anyway. 758 759 fdatasync=int Like fsync= but uses fdatasync() to only sync data and not 760 metadata blocks. 761 In FreeBSD and Windows there is no fdatasync(), this falls back to 762 using fsync() 763 764 sync_file_range=str:val Use sync_file_range() for every 'val' number of 765 write operations. Fio will track range of writes that 766 have happened since the last sync_file_range() call. 'str' 767 can currently be one or more of: 768 769 wait_before SYNC_FILE_RANGE_WAIT_BEFORE 770 write SYNC_FILE_RANGE_WRITE 771 wait_after SYNC_FILE_RANGE_WAIT_AFTER 772 773 So if you do sync_file_range=wait_before,write:8, fio would 774 use SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE for 775 every 8 writes. Also see the sync_file_range(2) man page. 776 This option is Linux specific. 777 778 overwrite=bool If true, writes to a file will always overwrite existing 779 data. If the file doesn't already exist, it will be 780 created before the write phase begins. If the file exists 781 and is large enough for the specified write phase, nothing 782 will be done. 783 784 end_fsync=bool If true, fsync file contents when a write stage has completed. 785 786 fsync_on_close=bool If true, fio will fsync() a dirty file on close. 787 This differs from end_fsync in that it will happen on every 788 file close, not just at the end of the job. 789 790 rwmixread=int How large a percentage of the mix should be reads. 791 792 rwmixwrite=int How large a percentage of the mix should be writes. If both 793 rwmixread and rwmixwrite is given and the values do not add 794 up to 100%, the latter of the two will be used to override 795 the first. This may interfere with a given rate setting, 796 if fio is asked to limit reads or writes to a certain rate. 797 If that is the case, then the distribution may be skewed. 798 799 random_distribution=str:float By default, fio will use a completely uniform 800 random distribution when asked to perform random IO. Sometimes 801 it is useful to skew the distribution in specific ways, 802 ensuring that some parts of the data is more hot than others. 803 fio includes the following distribution models: 804 805 random Uniform random distribution 806 zipf Zipf distribution 807 pareto Pareto distribution 808 809 When using a zipf or pareto distribution, an input value 810 is also needed to define the access pattern. For zipf, this 811 is the zipf theta. For pareto, it's the pareto power. Fio 812 includes a test program, genzipf, that can be used visualize 813 what the given input values will yield in terms of hit rates. 814 If you wanted to use zipf with a theta of 1.2, you would use 815 random_distribution=zipf:1.2 as the option. If a non-uniform 816 model is used, fio will disable use of the random map. 817 818 percentage_random=int For a random workload, set how big a percentage should 819 be random. This defaults to 100%, in which case the workload 820 is fully random. It can be set from anywhere from 0 to 100. 821 Setting it to 0 would make the workload fully sequential. Any 822 setting in between will result in a random mix of sequential 823 and random IO, at the given percentages. It is possible to 824 set different values for reads, writes, and trim. To do so, 825 simply use a comma separated list. See blocksize. 826 827 norandommap Normally fio will cover every block of the file when doing 828 random IO. If this option is given, fio will just get a 829 new random offset without looking at past io history. This 830 means that some blocks may not be read or written, and that 831 some blocks may be read/written more than once. This option 832 is mutually exclusive with verify= if and only if multiple 833 blocksizes (via bsrange=) are used, since fio only tracks 834 complete rewrites of blocks. 835 836 softrandommap=bool See norandommap. If fio runs with the random block map 837 enabled and it fails to allocate the map, if this option is 838 set it will continue without a random block map. As coverage 839 will not be as complete as with random maps, this option is 840 disabled by default. 841 842 random_generator=str Fio supports the following engines for generating 843 IO offsets for random IO: 844 845 tausworthe Strong 2^88 cycle random number generator 846 lfsr Linear feedback shift register generator 847 848 Tausworthe is a strong random number generator, but it 849 requires tracking on the side if we want to ensure that 850 blocks are only read or written once. LFSR guarantees 851 that we never generate the same offset twice, and it's 852 also less computationally expensive. It's not a true 853 random generator, however, though for IO purposes it's 854 typically good enough. LFSR only works with single 855 block sizes, not with workloads that use multiple block 856 sizes. If used with such a workload, fio may read or write 857 some blocks multiple times. 858 859 nice=int Run the job with the given nice value. See man nice(2). 860 861 prio=int Set the io priority value of this job. Linux limits us to 862 a positive value between 0 and 7, with 0 being the highest. 863 See man ionice(1). 864 865 prioclass=int Set the io priority class. See man ionice(1). 866 867 thinktime=int Stall the job x microseconds after an io has completed before 868 issuing the next. May be used to simulate processing being 869 done by an application. See thinktime_blocks and 870 thinktime_spin. 871 872 thinktime_spin=int 873 Only valid if thinktime is set - pretend to spend CPU time 874 doing something with the data received, before falling back 875 to sleeping for the rest of the period specified by 876 thinktime. 877 878 thinktime_blocks=int 879 Only valid if thinktime is set - control how many blocks 880 to issue, before waiting 'thinktime' usecs. If not set, 881 defaults to 1 which will make fio wait 'thinktime' usecs 882 after every block. This effectively makes any queue depth 883 setting redundant, since no more than 1 IO will be queued 884 before we have to complete it and do our thinktime. In 885 other words, this setting effectively caps the queue depth 886 if the latter is larger. 887 888 rate=int Cap the bandwidth used by this job. The number is in bytes/sec, 889 the normal suffix rules apply. You can use rate=500k to limit 890 reads and writes to 500k each, or you can specify read and 891 writes separately. Using rate=1m,500k would limit reads to 892 1MB/sec and writes to 500KB/sec. Capping only reads or 893 writes can be done with rate=,500k or rate=500k,. The former 894 will only limit writes (to 500KB/sec), the latter will only 895 limit reads. 896 897 ratemin=int Tell fio to do whatever it can to maintain at least this 898 bandwidth. Failing to meet this requirement, will cause 899 the job to exit. The same format as rate is used for 900 read vs write separation. 901 902 rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same 903 as rate, just specified independently of bandwidth. If the 904 job is given a block size range instead of a fixed value, 905 the smallest block size is used as the metric. The same format 906 as rate is used for read vs write separation. 907 908 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause 909 the job to exit. The same format as rate is used for read vs 910 write separation. 911 912 latency_target=int If set, fio will attempt to find the max performance 913 point that the given workload will run at while maintaining a 914 latency below this target. The values is given in microseconds. 915 See latency_window and latency_percentile 916 917 latency_window=int Used with latency_target to specify the sample window 918 that the job is run at varying queue depths to test the 919 performance. The value is given in microseconds. 920 921 latency_percentile=float The percentage of IOs that must fall within the 922 criteria specified by latency_target and latency_window. If not 923 set, this defaults to 100.0, meaning that all IOs must be equal 924 or below to the value set by latency_target. 925 926 max_latency=int If set, fio will exit the job if it exceeds this maximum 927 latency. It will exit with an ETIME error. 928 929 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number 930 of milliseconds. 931 932 cpumask=int Set the CPU affinity of this job. The parameter given is a 933 bitmask of allowed CPU's the job may run on. So if you want 934 the allowed CPUs to be 1 and 5, you would pass the decimal 935 value of (1 << 1 | 1 << 5), or 34. See man 936 sched_setaffinity(2). This may not work on all supported 937 operating systems or kernel versions. This option doesn't 938 work well for a higher CPU count than what you can store in 939 an integer mask, so it can only control cpus 1-32. For 940 boxes with larger CPU counts, use cpus_allowed. 941 942 cpus_allowed=str Controls the same options as cpumask, but it allows a text 943 setting of the permitted CPUs instead. So to use CPUs 1 and 944 5, you would specify cpus_allowed=1,5. This options also 945 allows a range of CPUs. Say you wanted a binding to CPUs 946 1, 5, and 8-15, you would set cpus_allowed=1,5,8-15. 947 948 cpus_allowed_policy=str Set the policy of how fio distributes the CPUs 949 specified by cpus_allowed or cpumask. Two policies are 950 supported: 951 952 shared All jobs will share the CPU set specified. 953 split Each job will get a unique CPU from the CPU set. 954 955 'shared' is the default behaviour, if the option isn't 956 specified. If split is specified, then fio will will assign 957 one cpu per job. If not enough CPUs are given for the jobs 958 listed, then fio will roundrobin the CPUs in the set. 959 960 numa_cpu_nodes=str Set this job running on spcified NUMA nodes' CPUs. The 961 arguments allow comma delimited list of cpu numbers, 962 A-B ranges, or 'all'. Note, to enable numa options support, 963 fio must be built on a system with libnuma-dev(el) installed. 964 965 numa_mem_policy=str Set this job's memory policy and corresponding NUMA 966 nodes. Format of the argements: 967 <mode>[:<nodelist>] 968 `mode' is one of the following memory policy: 969 default, prefer, bind, interleave, local 970 For `default' and `local' memory policy, no node is 971 needed to be specified. 972 For `prefer', only one node is allowed. 973 For `bind' and `interleave', it allow comma delimited 974 list of numbers, A-B ranges, or 'all'. 975 976 startdelay=time Start this job the specified number of seconds after fio 977 has started. Only useful if the job file contains several 978 jobs, and you want to delay starting some jobs to a certain 979 time. 980 981 runtime=time Tell fio to terminate processing after the specified number 982 of seconds. It can be quite hard to determine for how long 983 a specified job will run, so this parameter is handy to 984 cap the total runtime to a given time. 985 986 time_based If set, fio will run for the duration of the runtime 987 specified even if the file(s) are completely read or 988 written. It will simply loop over the same workload 989 as many times as the runtime allows. 990 991 ramp_time=time If set, fio will run the specified workload for this amount 992 of time before logging any performance numbers. Useful for 993 letting performance settle before logging results, thus 994 minimizing the runtime required for stable results. Note 995 that the ramp_time is considered lead in time for a job, 996 thus it will increase the total runtime if a special timeout 997 or runtime is specified. 998 999 invalidate=bool Invalidate the buffer/page cache parts for this file prior 1000 to starting io. Defaults to true. 1001 1002 sync=bool Use sync io for buffered writes. For the majority of the 1003 io engines, this means using O_SYNC. 1004 1005 iomem=str 1006 mem=str Fio can use various types of memory as the io unit buffer. 1007 The allowed values are: 1008 1009 malloc Use memory from malloc(3) as the buffers. 1010 1011 shm Use shared memory as the buffers. Allocated 1012 through shmget(2). 1013 1014 shmhuge Same as shm, but use huge pages as backing. 1015 1016 mmap Use mmap to allocate buffers. May either be 1017 anonymous memory, or can be file backed if 1018 a filename is given after the option. The 1019 format is mem=mmap:/path/to/file. 1020 1021 mmaphuge Use a memory mapped huge file as the buffer 1022 backing. Append filename after mmaphuge, ala 1023 mem=mmaphuge:/hugetlbfs/file 1024 1025 The area allocated is a function of the maximum allowed 1026 bs size for the job, multiplied by the io depth given. Note 1027 that for shmhuge and mmaphuge to work, the system must have 1028 free huge pages allocated. This can normally be checked 1029 and set by reading/writing /proc/sys/vm/nr_hugepages on a 1030 Linux system. Fio assumes a huge page is 4MB in size. So 1031 to calculate the number of huge pages you need for a given 1032 job file, add up the io depth of all jobs (normally one unless 1033 iodepth= is used) and multiply by the maximum bs set. Then 1034 divide that number by the huge page size. You can see the 1035 size of the huge pages in /proc/meminfo. If no huge pages 1036 are allocated by having a non-zero number in nr_hugepages, 1037 using mmaphuge or shmhuge will fail. Also see hugepage-size. 1038 1039 mmaphuge also needs to have hugetlbfs mounted and the file 1040 location should point there. So if it's mounted in /huge, 1041 you would use mem=mmaphuge:/huge/somefile. 1042 1043 iomem_align=int This indiciates the memory alignment of the IO memory buffers. 1044 Note that the given alignment is applied to the first IO unit 1045 buffer, if using iodepth the alignment of the following buffers 1046 are given by the bs used. In other words, if using a bs that is 1047 a multiple of the page sized in the system, all buffers will 1048 be aligned to this value. If using a bs that is not page 1049 aligned, the alignment of subsequent IO memory buffers is the 1050 sum of the iomem_align and bs used. 1051 1052 hugepage-size=int 1053 Defines the size of a huge page. Must at least be equal 1054 to the system setting, see /proc/meminfo. Defaults to 4MB. 1055 Should probably always be a multiple of megabytes, so using 1056 hugepage-size=Xm is the preferred way to set this to avoid 1057 setting a non-pow-2 bad value. 1058 1059 exitall When one job finishes, terminate the rest. The default is 1060 to wait for each job to finish, sometimes that is not the 1061 desired action. 1062 1063 bwavgtime=int Average the calculated bandwidth over the given time. Value 1064 is specified in milliseconds. 1065 1066 iopsavgtime=int Average the calculated IOPS over the given time. Value 1067 is specified in milliseconds. 1068 1069 create_serialize=bool If true, serialize the file creating for the jobs. 1070 This may be handy to avoid interleaving of data 1071 files, which may greatly depend on the filesystem 1072 used and even the number of processors in the system. 1073 1074 create_fsync=bool fsync the data file after creation. This is the 1075 default. 1076 1077 create_on_open=bool Don't pre-setup the files for IO, just create open() 1078 when it's time to do IO to that file. 1079 1080 create_only=bool If true, fio will only run the setup phase of the job. 1081 If files need to be laid out or updated on disk, only 1082 that will be done. The actual job contents are not 1083 executed. 1084 1085 pre_read=bool If this is given, files will be pre-read into memory before 1086 starting the given IO operation. This will also clear 1087 the 'invalidate' flag, since it is pointless to pre-read 1088 and then drop the cache. This will only work for IO engines 1089 that are seekable, since they allow you to read the same data 1090 multiple times. Thus it will not work on eg network or splice 1091 IO. 1092 1093 unlink=bool Unlink the job files when done. Not the default, as repeated 1094 runs of that job would then waste time recreating the file 1095 set again and again. 1096 1097 loops=int Run the specified number of iterations of this job. Used 1098 to repeat the same workload a given number of times. Defaults 1099 to 1. 1100 1101 verify_only Do not perform specified workload---only verify data still 1102 matches previous invocation of this workload. This option 1103 allows one to check data multiple times at a later date 1104 without overwriting it. This option makes sense only for 1105 workloads that write data, and does not support workloads 1106 with the time_based option set. 1107 1108 do_verify=bool Run the verify phase after a write phase. Only makes sense if 1109 verify is set. Defaults to 1. 1110 1111 verify=str If writing to a file, fio can verify the file contents 1112 after each iteration of the job. The allowed values are: 1113 1114 md5 Use an md5 sum of the data area and store 1115 it in the header of each block. 1116 1117 crc64 Use an experimental crc64 sum of the data 1118 area and store it in the header of each 1119 block. 1120 1121 crc32c Use a crc32c sum of the data area and store 1122 it in the header of each block. 1123 1124 crc32c-intel Use hardware assisted crc32c calcuation 1125 provided on SSE4.2 enabled processors. Falls 1126 back to regular software crc32c, if not 1127 supported by the system. 1128 1129 crc32 Use a crc32 sum of the data area and store 1130 it in the header of each block. 1131 1132 crc16 Use a crc16 sum of the data area and store 1133 it in the header of each block. 1134 1135 crc7 Use a crc7 sum of the data area and store 1136 it in the header of each block. 1137 1138 xxhash Use xxhash as the checksum function. Generally 1139 the fastest software checksum that fio 1140 supports. 1141 1142 sha512 Use sha512 as the checksum function. 1143 1144 sha256 Use sha256 as the checksum function. 1145 1146 sha1 Use optimized sha1 as the checksum function. 1147 1148 meta Write extra information about each io 1149 (timestamp, block number etc.). The block 1150 number is verified. The io sequence number is 1151 verified for workloads that write data. 1152 See also verify_pattern. 1153 1154 null Only pretend to verify. Useful for testing 1155 internals with ioengine=null, not for much 1156 else. 1157 1158 This option can be used for repeated burn-in tests of a 1159 system to make sure that the written data is also 1160 correctly read back. If the data direction given is 1161 a read or random read, fio will assume that it should 1162 verify a previously written file. If the data direction 1163 includes any form of write, the verify will be of the 1164 newly written data. 1165 1166 verifysort=bool If set, fio will sort written verify blocks when it deems 1167 it faster to read them back in a sorted manner. This is 1168 often the case when overwriting an existing file, since 1169 the blocks are already laid out in the file system. You 1170 can ignore this option unless doing huge amounts of really 1171 fast IO where the red-black tree sorting CPU time becomes 1172 significant. 1173 1174 verify_offset=int Swap the verification header with data somewhere else 1175 in the block before writing. Its swapped back before 1176 verifying. 1177 1178 verify_interval=int Write the verification header at a finer granularity 1179 than the blocksize. It will be written for chunks the 1180 size of header_interval. blocksize should divide this 1181 evenly. 1182 1183 verify_pattern=str If set, fio will fill the io buffers with this 1184 pattern. Fio defaults to filling with totally random 1185 bytes, but sometimes it's interesting to fill with a known 1186 pattern for io verification purposes. Depending on the 1187 width of the pattern, fio will fill 1/2/3/4 bytes of the 1188 buffer at the time(it can be either a decimal or a hex number). 1189 The verify_pattern if larger than a 32-bit quantity has to 1190 be a hex number that starts with either "0x" or "0X". Use 1191 with verify=meta. 1192 1193 verify_fatal=bool Normally fio will keep checking the entire contents 1194 before quitting on a block verification failure. If this 1195 option is set, fio will exit the job on the first observed 1196 failure. 1197 1198 verify_dump=bool If set, dump the contents of both the original data 1199 block and the data block we read off disk to files. This 1200 allows later analysis to inspect just what kind of data 1201 corruption occurred. Off by default. 1202 1203 verify_async=int Fio will normally verify IO inline from the submitting 1204 thread. This option takes an integer describing how many 1205 async offload threads to create for IO verification instead, 1206 causing fio to offload the duty of verifying IO contents 1207 to one or more separate threads. If using this offload 1208 option, even sync IO engines can benefit from using an 1209 iodepth setting higher than 1, as it allows them to have 1210 IO in flight while verifies are running. 1211 1212 verify_async_cpus=str Tell fio to set the given CPU affinity on the 1213 async IO verification threads. See cpus_allowed for the 1214 format used. 1215 1216 verify_backlog=int Fio will normally verify the written contents of a 1217 job that utilizes verify once that job has completed. In 1218 other words, everything is written then everything is read 1219 back and verified. You may want to verify continually 1220 instead for a variety of reasons. Fio stores the meta data 1221 associated with an IO block in memory, so for large 1222 verify workloads, quite a bit of memory would be used up 1223 holding this meta data. If this option is enabled, fio 1224 will write only N blocks before verifying these blocks. 1225 1226 verify_backlog_batch=int Control how many blocks fio will verify 1227 if verify_backlog is set. If not set, will default to 1228 the value of verify_backlog (meaning the entire queue 1229 is read back and verified). If verify_backlog_batch is 1230 less than verify_backlog then not all blocks will be verified, 1231 if verify_backlog_batch is larger than verify_backlog, some 1232 blocks will be verified more than once. 1233 1234 stonewall 1235 wait_for_previous Wait for preceding jobs in the job file to exit, before 1236 starting this one. Can be used to insert serialization 1237 points in the job file. A stone wall also implies starting 1238 a new reporting group. 1239 1240 new_group Start a new reporting group. See: group_reporting. 1241 1242 numjobs=int Create the specified number of clones of this job. May be 1243 used to setup a larger number of threads/processes doing 1244 the same thing. Each thread is reported separately; to see 1245 statistics for all clones as a whole, use group_reporting in 1246 conjunction with new_group. 1247 1248 group_reporting It may sometimes be interesting to display statistics for 1249 groups of jobs as a whole instead of for each individual job. 1250 This is especially true if 'numjobs' is used; looking at 1251 individual thread/process output quickly becomes unwieldy. 1252 To see the final report per-group instead of per-job, use 1253 'group_reporting'. Jobs in a file will be part of the same 1254 reporting group, unless if separated by a stonewall, or by 1255 using 'new_group'. 1256 1257 thread fio defaults to forking jobs, however if this option is 1258 given, fio will use pthread_create(3) to create threads 1259 instead. 1260 1261 zonesize=int Divide a file into zones of the specified size. See zoneskip. 1262 1263 zoneskip=int Skip the specified number of bytes when zonesize data has 1264 been read. The two zone options can be used to only do 1265 io on zones of a file. 1266 1267 write_iolog=str Write the issued io patterns to the specified file. See 1268 read_iolog. Specify a separate file for each job, otherwise 1269 the iologs will be interspersed and the file may be corrupt. 1270 1271 read_iolog=str Open an iolog with the specified file name and replay the 1272 io patterns it contains. This can be used to store a 1273 workload and replay it sometime later. The iolog given 1274 may also be a blktrace binary file, which allows fio 1275 to replay a workload captured by blktrace. See blktrace 1276 for how to capture such logging data. For blktrace replay, 1277 the file needs to be turned into a blkparse binary data 1278 file first (blkparse <device> -o /dev/null -d file_for_fio.bin). 1279 1280 replay_no_stall=int When replaying I/O with read_iolog the default behavior 1281 is to attempt to respect the time stamps within the log and 1282 replay them with the appropriate delay between IOPS. By 1283 setting this variable fio will not respect the timestamps and 1284 attempt to replay them as fast as possible while still 1285 respecting ordering. The result is the same I/O pattern to a 1286 given device, but different timings. 1287 1288 replay_redirect=str While replaying I/O patterns using read_iolog the 1289 default behavior is to replay the IOPS onto the major/minor 1290 device that each IOP was recorded from. This is sometimes 1291 undesirable because on a different machine those major/minor 1292 numbers can map to a different device. Changing hardware on 1293 the same system can also result in a different major/minor 1294 mapping. Replay_redirect causes all IOPS to be replayed onto 1295 the single specified device regardless of the device it was 1296 recorded from. i.e. replay_redirect=/dev/sdc would cause all 1297 IO in the blktrace to be replayed onto /dev/sdc. This means 1298 multiple devices will be replayed onto a single, if the trace 1299 contains multiple devices. If you want multiple devices to be 1300 replayed concurrently to multiple redirected devices you must 1301 blkparse your trace into separate traces and replay them with 1302 independent fio invocations. Unfortuantely this also breaks 1303 the strict time ordering between multiple device accesses. 1304 1305 write_bw_log=str If given, write a bandwidth log of the jobs in this job 1306 file. Can be used to store data of the bandwidth of the 1307 jobs in their lifetime. The included fio_generate_plots 1308 script uses gnuplot to turn these text files into nice 1309 graphs. See write_lat_log for behaviour of given 1310 filename. For this option, the suffix is _bw.log. 1311 1312 write_lat_log=str Same as write_bw_log, except that this option stores io 1313 submission, completion, and total latencies instead. If no 1314 filename is given with this option, the default filename of 1315 "jobname_type.log" is used. Even if the filename is given, 1316 fio will still append the type of log. So if one specifies 1317 1318 write_lat_log=foo 1319 1320 The actual log names will be foo_slat.log, foo_clat.log, 1321 and foo_lat.log. This helps fio_generate_plot fine the logs 1322 automatically. 1323 1324 write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is 1325 given with this option, the default filename of 1326 "jobname_type.log" is used. Even if the filename is given, 1327 fio will still append the type of log. 1328 1329 log_avg_msec=int By default, fio will log an entry in the iops, latency, 1330 or bw log for every IO that completes. When writing to the 1331 disk log, that can quickly grow to a very large size. Setting 1332 this option makes fio average the each log entry over the 1333 specified period of time, reducing the resolution of the log. 1334 Defaults to 0. 1335 1336 lockmem=int Pin down the specified amount of memory with mlock(2). Can 1337 potentially be used instead of removing memory or booting 1338 with less memory to simulate a smaller amount of memory. 1339 The amount specified is per worker. 1340 1341 exec_prerun=str Before running this job, issue the command specified 1342 through system(3). Output is redirected in a file called 1343 jobname.prerun.txt. 1344 1345 exec_postrun=str After the job completes, issue the command specified 1346 though system(3). Output is redirected in a file called 1347 jobname.postrun.txt. 1348 1349 ioscheduler=str Attempt to switch the device hosting the file to the specified 1350 io scheduler before running. 1351 1352 disk_util=bool Generate disk utilization statistics, if the platform 1353 supports it. Defaults to on. 1354 1355 disable_lat=bool Disable measurements of total latency numbers. Useful 1356 only for cutting back the number of calls to gettimeofday, 1357 as that does impact performance at really high IOPS rates. 1358 Note that to really get rid of a large amount of these 1359 calls, this option must be used with disable_slat and 1360 disable_bw as well. 1361 1362 disable_clat=bool Disable measurements of completion latency numbers. See 1363 disable_lat. 1364 1365 disable_slat=bool Disable measurements of submission latency numbers. See 1366 disable_slat. 1367 1368 disable_bw=bool Disable measurements of throughput/bandwidth numbers. See 1369 disable_lat. 1370 1371 clat_percentiles=bool Enable the reporting of percentiles of 1372 completion latencies. 1373 1374 percentile_list=float_list Overwrite the default list of percentiles 1375 for completion latencies. Each number is a floating 1376 number in the range (0,100], and the maximum length of 1377 the list is 20. Use ':' to separate the numbers, and 1378 list the numbers in ascending order. For example, 1379 --percentile_list=99.5:99.9 will cause fio to report 1380 the values of completion latency below which 99.5% and 1381 99.9% of the observed latencies fell, respectively. 1382 1383 clocksource=str Use the given clocksource as the base of timing. The 1384 supported options are: 1385 1386 gettimeofday gettimeofday(2) 1387 1388 clock_gettime clock_gettime(2) 1389 1390 cpu Internal CPU clock source 1391 1392 cpu is the preferred clocksource if it is reliable, as it 1393 is very fast (and fio is heavy on time calls). Fio will 1394 automatically use this clocksource if it's supported and 1395 considered reliable on the system it is running on, unless 1396 another clocksource is specifically set. For x86/x86-64 CPUs, 1397 this means supporting TSC Invariant. 1398 1399 gtod_reduce=bool Enable all of the gettimeofday() reducing options 1400 (disable_clat, disable_slat, disable_bw) plus reduce 1401 precision of the timeout somewhat to really shrink 1402 the gettimeofday() call count. With this option enabled, 1403 we only do about 0.4% of the gtod() calls we would have 1404 done if all time keeping was enabled. 1405 1406 gtod_cpu=int Sometimes it's cheaper to dedicate a single thread of 1407 execution to just getting the current time. Fio (and 1408 databases, for instance) are very intensive on gettimeofday() 1409 calls. With this option, you can set one CPU aside for 1410 doing nothing but logging current time to a shared memory 1411 location. Then the other threads/processes that run IO 1412 workloads need only copy that segment, instead of entering 1413 the kernel with a gettimeofday() call. The CPU set aside 1414 for doing these time calls will be excluded from other 1415 uses. Fio will manually clear it from the CPU mask of other 1416 jobs. 1417 1418 continue_on_error=str Normally fio will exit the job on the first observed 1419 failure. If this option is set, fio will continue the job when 1420 there is a 'non-fatal error' (EIO or EILSEQ) until the runtime 1421 is exceeded or the I/O size specified is completed. If this 1422 option is used, there are two more stats that are appended, 1423 the total error count and the first error. The error field 1424 given in the stats is the first error that was hit during the 1425 run. 1426 1427 The allowed values are: 1428 1429 none Exit on any IO or verify errors. 1430 1431 read Continue on read errors, exit on all others. 1432 1433 write Continue on write errors, exit on all others. 1434 1435 io Continue on any IO error, exit on all others. 1436 1437 verify Continue on verify errors, exit on all others. 1438 1439 all Continue on all errors. 1440 1441 0 Backward-compatible alias for 'none'. 1442 1443 1 Backward-compatible alias for 'all'. 1444 1445 ignore_error=str Sometimes you want to ignore some errors during test 1446 in that case you can specify error list for each error type. 1447 ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST 1448 errors for given error type is separated with ':'. Error 1449 may be symbol ('ENOSPC', 'ENOMEM') or integer. 1450 Example: 1451 ignore_error=EAGAIN,ENOSPC:122 1452 This option will ignore EAGAIN from READ, and ENOSPC and 1453 122(EDQUOT) from WRITE. 1454 1455 error_dump=bool If set dump every error even if it is non fatal, true 1456 by default. If disabled only fatal error will be dumped 1457 1458 cgroup=str Add job to this control group. If it doesn't exist, it will 1459 be created. The system must have a mounted cgroup blkio 1460 mount point for this to work. If your system doesn't have it 1461 mounted, you can do so with: 1462 1463 # mount -t cgroup -o blkio none /cgroup 1464 1465 cgroup_weight=int Set the weight of the cgroup to this value. See 1466 the documentation that comes with the kernel, allowed values 1467 are in the range of 100..1000. 1468 1469 cgroup_nodelete=bool Normally fio will delete the cgroups it has created after 1470 the job completion. To override this behavior and to leave 1471 cgroups around after the job completion, set cgroup_nodelete=1. 1472 This can be useful if one wants to inspect various cgroup 1473 files after job completion. Default: false 1474 1475 uid=int Instead of running as the invoking user, set the user ID to 1476 this value before the thread/process does any work. 1477 1478 gid=int Set group ID, see uid. 1479 1480 flow_id=int The ID of the flow. If not specified, it defaults to being a 1481 global flow. See flow. 1482 1483 flow=int Weight in token-based flow control. If this value is used, then 1484 there is a 'flow counter' which is used to regulate the 1485 proportion of activity between two or more jobs. fio attempts 1486 to keep this flow counter near zero. The 'flow' parameter 1487 stands for how much should be added or subtracted to the flow 1488 counter on each iteration of the main I/O loop. That is, if 1489 one job has flow=8 and another job has flow=-1, then there 1490 will be a roughly 1:8 ratio in how much one runs vs the other. 1491 1492 flow_watermark=int The maximum value that the absolute value of the flow 1493 counter is allowed to reach before the job must wait for a 1494 lower value of the counter. 1495 1496 flow_sleep=int The period of time, in microseconds, to wait after the flow 1497 watermark has been exceeded before retrying operations 1498 1499 In addition, there are some parameters which are only valid when a specific 1500 ioengine is in use. These are used identically to normal parameters, with the 1501 caveat that when used on the command line, they must come after the ioengine 1502 that defines them is selected. 1503 1504 [libaio] userspace_reap Normally, with the libaio engine in use, fio will use 1505 the io_getevents system call to reap newly returned events. 1506 With this flag turned on, the AIO ring will be read directly 1507 from user-space to reap events. The reaping mode is only 1508 enabled when polling for a minimum of 0 events (eg when 1509 iodepth_batch_complete=0). 1510 1511 [cpu] cpuload=int Attempt to use the specified percentage of CPU cycles. 1512 1513 [cpu] cpuchunks=int Split the load into cycles of the given time. In 1514 microseconds. 1515 1516 [cpu] exit_on_io_done=bool Detect when IO threads are done, then exit. 1517 1518 [netsplice] hostname=str 1519 [net] hostname=str The host name or IP address to use for TCP or UDP based IO. 1520 If the job is a TCP listener or UDP reader, the hostname is not 1521 used and must be omitted unless it is a valid UDP multicast 1522 address. 1523 1524 [netsplice] port=int 1525 [net] port=int The TCP or UDP port to bind to or connect to. 1526 1527 [netsplice] interface=str 1528 [net] interface=str The IP address of the network interface used to send or 1529 receive UDP multicast 1530 1531 [netsplice] ttl=int 1532 [net] ttl=int Time-to-live value for outgoing UDP multicast packets. 1533 Default: 1 1534 1535 [netsplice] nodelay=bool 1536 [net] nodelay=bool Set TCP_NODELAY on TCP connections. 1537 1538 [netsplice] protocol=str 1539 [netsplice] proto=str 1540 [net] protocol=str 1541 [net] proto=str The network protocol to use. Accepted values are: 1542 1543 tcp Transmission control protocol 1544 tcpv6 Transmission control protocol V6 1545 udp User datagram protocol 1546 udpv6 User datagram protocol V6 1547 unix UNIX domain socket 1548 1549 When the protocol is TCP or UDP, the port must also be given, 1550 as well as the hostname if the job is a TCP listener or UDP 1551 reader. For unix sockets, the normal filename option should be 1552 used and the port is invalid. 1553 1554 [net] listen For TCP network connections, tell fio to listen for incoming 1555 connections rather than initiating an outgoing connection. The 1556 hostname must be omitted if this option is used. 1557 [net] pingpong Normaly a network writer will just continue writing data, and 1558 a network reader will just consume packages. If pingpong=1 1559 is set, a writer will send its normal payload to the reader, 1560 then wait for the reader to send the same payload back. This 1561 allows fio to measure network latencies. The submission 1562 and completion latencies then measure local time spent 1563 sending or receiving, and the completion latency measures 1564 how long it took for the other end to receive and send back. 1565 For UDP multicast traffic pingpong=1 should only be set for a 1566 single reader when multiple readers are listening to the same 1567 address. 1568 1569 [e4defrag] donorname=str 1570 File will be used as a block donor(swap extents between files) 1571 [e4defrag] inplace=int 1572 Configure donor file blocks allocation strategy 1573 0(default): Preallocate donor's file on init 1574 1 : allocate space immidietly inside defragment event, 1575 and free right after event 1576 1577 1578 1579 6.0 Interpreting the output 1580 --------------------------- 1581 1582 fio spits out a lot of output. While running, fio will display the 1583 status of the jobs created. An example of that would be: 1584 1585 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s] 1586 1587 The characters inside the square brackets denote the current status of 1588 each thread. The possible values (in typical life cycle order) are: 1589 1590 Idle Run 1591 ---- --- 1592 P Thread setup, but not started. 1593 C Thread created. 1594 I Thread initialized, waiting or generating necessary data. 1595 p Thread running pre-reading file(s). 1596 R Running, doing sequential reads. 1597 r Running, doing random reads. 1598 W Running, doing sequential writes. 1599 w Running, doing random writes. 1600 M Running, doing mixed sequential reads/writes. 1601 m Running, doing mixed random reads/writes. 1602 F Running, currently waiting for fsync() 1603 f Running, finishing up (writing IO logs, etc) 1604 V Running, doing verification of written data. 1605 E Thread exited, not reaped by main thread yet. 1606 _ Thread reaped, or 1607 X Thread reaped, exited with an error. 1608 K Thread reaped, exited due to signal. 1609 1610 The other values are fairly self explanatory - number of threads 1611 currently running and doing io, rate of io since last check (read speed 1612 listed first, then write speed), and the estimated completion percentage 1613 and time for the running group. It's impossible to estimate runtime of 1614 the following groups (if any). Note that the string is displayed in order, 1615 so it's possible to tell which of the jobs are currently doing what. The 1616 first character is the first job defined in the job file, and so forth. 1617 1618 When fio is done (or interrupted by ctrl-c), it will show the data for 1619 each thread, group of threads, and disks in that order. For each data 1620 direction, the output looks like: 1621 1622 Client1 (g=0): err= 0: 1623 write: io= 32MB, bw= 666KB/s, iops=89 , runt= 50320msec 1624 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92 1625 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82 1626 bw (KB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68 1627 cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17 1628 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0% 1629 submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% 1630 complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% 1631 issued r/w: total=0/32768, short=0/0 1632 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%, 1633 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0% 1634 1635 The client number is printed, along with the group id and error of that 1636 thread. Below is the io statistics, here for writes. In the order listed, 1637 they denote: 1638 1639 io= Number of megabytes io performed 1640 bw= Average bandwidth rate 1641 iops= Average IOs performed per second 1642 runt= The runtime of that thread 1643 slat= Submission latency (avg being the average, stdev being the 1644 standard deviation). This is the time it took to submit 1645 the io. For sync io, the slat is really the completion 1646 latency, since queue/complete is one operation there. This 1647 value can be in milliseconds or microseconds, fio will choose 1648 the most appropriate base and print that. In the example 1649 above, milliseconds is the best scale. Note: in --minimal mode 1650 latencies are always expressed in microseconds. 1651 clat= Completion latency. Same names as slat, this denotes the 1652 time from submission to completion of the io pieces. For 1653 sync io, clat will usually be equal (or very close) to 0, 1654 as the time from submit to complete is basically just 1655 CPU time (io has already been done, see slat explanation). 1656 bw= Bandwidth. Same names as the xlat stats, but also includes 1657 an approximate percentage of total aggregate bandwidth 1658 this thread received in this group. This last value is 1659 only really useful if the threads in this group are on the 1660 same disk, since they are then competing for disk access. 1661 cpu= CPU usage. User and system time, along with the number 1662 of context switches this thread went through, usage of 1663 system and user time, and finally the number of major 1664 and minor page faults. 1665 IO depths= The distribution of io depths over the job life time. The 1666 numbers are divided into powers of 2, so for example the 1667 16= entries includes depths up to that value but higher 1668 than the previous entry. In other words, it covers the 1669 range from 16 to 31. 1670 IO submit= How many pieces of IO were submitting in a single submit 1671 call. Each entry denotes that amount and below, until 1672 the previous entry - eg, 8=100% mean that we submitted 1673 anywhere in between 5-8 ios per submit call. 1674 IO complete= Like the above submit number, but for completions instead. 1675 IO issued= The number of read/write requests issued, and how many 1676 of them were short. 1677 IO latencies= The distribution of IO completion latencies. This is the 1678 time from when IO leaves fio and when it gets completed. 1679 The numbers follow the same pattern as the IO depths, 1680 meaning that 2=1.6% means that 1.6% of the IO completed 1681 within 2 msecs, 20=12.8% means that 12.8% of the IO 1682 took more than 10 msecs, but less than (or equal to) 20 msecs. 1683 1684 After each client has been listed, the group statistics are printed. They 1685 will look like this: 1686 1687 Run status group 0 (all jobs): 1688 READ: io=64MB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec 1689 WRITE: io=64MB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec 1690 1691 For each data direction, it prints: 1692 1693 io= Number of megabytes io performed. 1694 aggrb= Aggregate bandwidth of threads in this group. 1695 minb= The minimum average bandwidth a thread saw. 1696 maxb= The maximum average bandwidth a thread saw. 1697 mint= The smallest runtime of the threads in that group. 1698 maxt= The longest runtime of the threads in that group. 1699 1700 And finally, the disk statistics are printed. They will look like this: 1701 1702 Disk stats (read/write): 1703 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00% 1704 1705 Each value is printed for both reads and writes, with reads first. The 1706 numbers denote: 1707 1708 ios= Number of ios performed by all groups. 1709 merge= Number of merges io the io scheduler. 1710 ticks= Number of ticks we kept the disk busy. 1711 io_queue= Total time spent in the disk queue. 1712 util= The disk utilization. A value of 100% means we kept the disk 1713 busy constantly, 50% would be a disk idling half of the time. 1714 1715 It is also possible to get fio to dump the current output while it is 1716 running, without terminating the job. To do that, send fio the USR1 signal. 1717 You can also get regularly timed dumps by using the --status-interval 1718 parameter, or by creating a file in /tmp named fio-dump-status. If fio 1719 sees this file, it will unlink it and dump the current output status. 1720 1721 1722 7.0 Terse output 1723 ---------------- 1724 1725 For scripted usage where you typically want to generate tables or graphs 1726 of the results, fio can output the results in a semicolon separated format. 1727 The format is one long line of values, such as: 1728 1729 2;card0;0;0;7139336;121836;60004;1;10109;27.932460;116.933948;220;126861;3495.446807;1085.368601;226;126864;3523.635629;1089.012448;24063;99944;50.275485%;59818.274627;5540.657370;7155060;122104;60004;1;8338;29.086342;117.839068;388;128077;5032.488518;1234.785715;391;128085;5061.839412;1236.909129;23436;100928;50.287926%;59964.832030;5644.844189;14.595833%;19.394167%;123706;0;7313;0.1%;0.1%;0.1%;0.1%;0.1%;0.1%;100.0%;0.00%;0.00%;0.00%;0.00%;0.00%;0.00%;0.01%;0.02%;0.05%;0.16%;6.04%;40.40%;52.68%;0.64%;0.01%;0.00%;0.01%;0.00%;0.00%;0.00%;0.00%;0.00% 1730 A description of this job goes here. 1731 1732 The job description (if provided) follows on a second line. 1733 1734 To enable terse output, use the --minimal command line option. The first 1735 value is the version of the terse output format. If the output has to 1736 be changed for some reason, this number will be incremented by 1 to 1737 signify that change. 1738 1739 Split up, the format is as follows: 1740 1741 terse version, fio version, jobname, groupid, error 1742 READ status: 1743 Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec) 1744 Submission latency: min, max, mean, deviation (usec) 1745 Completion latency: min, max, mean, deviation (usec) 1746 Completion latency percentiles: 20 fields (see below) 1747 Total latency: min, max, mean, deviation (usec) 1748 Bw (KB/s): min, max, aggregate percentage of total, mean, deviation 1749 WRITE status: 1750 Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec) 1751 Submission latency: min, max, mean, deviation (usec) 1752 Completion latency: min, max, mean, deviation (usec) 1753 Completion latency percentiles: 20 fields (see below) 1754 Total latency: min, max, mean, deviation (usec) 1755 Bw (KB/s): min, max, aggregate percentage of total, mean, deviation 1756 CPU usage: user, system, context switches, major faults, minor faults 1757 IO depths: <=1, 2, 4, 8, 16, 32, >=64 1758 IO latencies microseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000 1759 IO latencies milliseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000 1760 Disk utilization: Disk name, Read ios, write ios, 1761 Read merges, write merges, 1762 Read ticks, write ticks, 1763 Time spent in queue, disk utilization percentage 1764 Additional Info (dependent on continue_on_error, default off): total # errors, first error code 1765 1766 Additional Info (dependent on description being set): Text description 1767 1768 Completion latency percentiles can be a grouping of up to 20 sets, so 1769 for the terse output fio writes all of them. Each field will look like this: 1770 1771 1.00%=6112 1772 1773 which is the Xth percentile, and the usec latency associated with it. 1774 1775 For disk utilization, all disks used by fio are shown. So for each disk 1776 there will be a disk utilization section. 1777 1778 1779 8.0 Trace file format 1780 --------------------- 1781 There are two trace file format that you can encounter. The older (v1) format 1782 is unsupported since version 1.20-rc3 (March 2008). It will still be described 1783 below in case that you get an old trace and want to understand it. 1784 1785 In any case the trace is a simple text file with a single action per line. 1786 1787 1788 8.1 Trace file format v1 1789 ------------------------ 1790 Each line represents a single io action in the following format: 1791 1792 rw, offset, length 1793 1794 where rw=0/1 for read/write, and the offset and length entries being in bytes. 1795 1796 This format is not supported in Fio versions => 1.20-rc3. 1797 1798 1799 8.2 Trace file format v2 1800 ------------------------ 1801 The second version of the trace file format was added in Fio version 1.17. 1802 It allows to access more then one file per trace and has a bigger set of 1803 possible file actions. 1804 1805 The first line of the trace file has to be: 1806 1807 fio version 2 iolog 1808 1809 Following this can be lines in two different formats, which are described below. 1810 1811 The file management format: 1812 1813 filename action 1814 1815 The filename is given as an absolute path. The action can be one of these: 1816 1817 add Add the given filename to the trace 1818 open Open the file with the given filename. The filename has to have 1819 been added with the add action before. 1820 close Close the file with the given filename. The file has to have been 1821 opened before. 1822 1823 1824 The file io action format: 1825 1826 filename action offset length 1827 1828 The filename is given as an absolute path, and has to have been added and opened 1829 before it can be used with this format. The offset and length are given in 1830 bytes. The action can be one of these: 1831 1832 wait Wait for 'offset' microseconds. Everything below 100 is discarded. 1833 read Read 'length' bytes beginning from 'offset' 1834 write Write 'length' bytes beginning from 'offset' 1835 sync fsync() the file 1836 datasync fdatasync() the file 1837 trim trim the given file from the given 'offset' for 'length' bytes 1838 1839 1840 9.0 CPU idleness profiling 1841 -------------------------- 1842 In some cases, we want to understand CPU overhead in a test. For example, 1843 we test patches for the specific goodness of whether they reduce CPU usage. 1844 fio implements a balloon approach to create a thread per CPU that runs at 1845 idle priority, meaning that it only runs when nobody else needs the cpu. 1846 By measuring the amount of work completed by the thread, idleness of each 1847 CPU can be derived accordingly. 1848 1849 An unit work is defined as touching a full page of unsigned characters. Mean 1850 and standard deviation of time to complete an unit work is reported in "unit 1851 work" section. Options can be chosen to report detailed percpu idleness or 1852 overall system idleness by aggregating percpu stats. 1853
