1 Demonstrations of llcstat. 2 3 4 llcstat traces cache reference and cache miss events system-wide, and summarizes 5 them by PID and CPU. 6 7 These events, defined in uapi/linux/perf_event.h, have different meanings on 8 different architecture. For x86-64, they mean misses and references to LLC. 9 10 Example output: 11 12 # ./llcstat.py 20 -c 5000 13 Running for 20 seconds or hit Ctrl-C to end. 14 PID NAME CPU REFERENCE MISS HIT% 15 0 swapper/15 15 3515000 640000 81.79% 16 238 migration/38 38 5000 0 100.00% 17 4512 ntpd 11 5000 0 100.00% 18 150867 ipmitool 3 25000 5000 80.00% 19 150895 lscpu 17 280000 25000 91.07% 20 151807 ipmitool 15 15000 5000 66.67% 21 150757 awk 2 15000 5000 66.67% 22 151213 chef-client 5 1770000 240000 86.44% 23 151822 scribe-dispatch 12 15000 0 100.00% 24 123386 mysqld 5 5000 0 100.00% 25 [...] 26 Total References: 518920000 Total Misses: 90265000 Hit Rate: 82.61% 27 28 This shows each PID's cache hit rate during the 20 seconds run period. 29 30 A count of 5000 was used in this example, which means that one in every 5,000 31 events will trigger an in-kernel counter to be incremented. This is refactored 32 on the output, which is why it is always in multiples of 5,000. 33 34 We don't instrument every single event since the overhead would be prohibitive, 35 nor do we need to: this is a type of sampling profiler. Because of this, the 36 processes that trigger the 5,000'th cache reference or misses can happen to 37 some degree by chance. Overall it should make sense. But for low counts, 38 you might find a case where -- by chance -- a process has been tallied with 39 more misses than references, which would seem impossible. 40 41 42 USAGE message: 43 44 # ./llcstat.py --help 45 usage: llcstat.py [-h] [-c SAMPLE_PERIOD] [duration] 46 47 Summarize cache references and misses by PID 48 49 positional arguments: 50 duration Duration, in seconds, to run 51 52 optional arguments: 53 -h, --help show this help message and exit 54 -c SAMPLE_PERIOD, --sample_period SAMPLE_PERIOD 55 Sample one in this many number of cache reference 56 and miss events 57
