1 #ifndef _LINUX_JIFFIES_H 2 #define _LINUX_JIFFIES_H 3 4 #include <linux/calc64.h> 5 #include <linux/kernel.h> 6 #include <linux/types.h> 7 #include <linux/time.h> 8 #include <linux/timex.h> 9 #include <asm/param.h> /* for HZ */ 10 11 /* 12 * The following defines establish the engineering parameters of the PLL 13 * model. The HZ variable establishes the timer interrupt frequency, 100 Hz 14 * for the SunOS kernel, 256 Hz for the Ultrix kernel and 1024 Hz for the 15 * OSF/1 kernel. The SHIFT_HZ define expresses the same value as the 16 * nearest power of two in order to avoid hardware multiply operations. 17 */ 18 #if HZ >= 12 && HZ < 24 19 # define SHIFT_HZ 4 20 #elif HZ >= 24 && HZ < 48 21 # define SHIFT_HZ 5 22 #elif HZ >= 48 && HZ < 96 23 # define SHIFT_HZ 6 24 #elif HZ >= 96 && HZ < 192 25 # define SHIFT_HZ 7 26 #elif HZ >= 192 && HZ < 384 27 # define SHIFT_HZ 8 28 #elif HZ >= 384 && HZ < 768 29 # define SHIFT_HZ 9 30 #elif HZ >= 768 && HZ < 1536 31 # define SHIFT_HZ 10 32 #else 33 # error You lose. 34 #endif 35 36 /* LATCH is used in the interval timer and ftape setup. */ 37 #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */ 38 39 #define LATCH_HPET ((HPET_TICK_RATE + HZ/2) / HZ) 40 41 /* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, the we can 42 * improve accuracy by shifting LSH bits, hence calculating: 43 * (NOM << LSH) / DEN 44 * This however means trouble for large NOM, because (NOM << LSH) may no 45 * longer fit in 32 bits. The following way of calculating this gives us 46 * some slack, under the following conditions: 47 * - (NOM / DEN) fits in (32 - LSH) bits. 48 * - (NOM % DEN) fits in (32 - LSH) bits. 49 */ 50 #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \ 51 + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN)) 52 53 /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */ 54 #define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8)) 55 56 #define ACTHZ_HPET (SH_DIV (HPET_TICK_RATE, LATCH_HPET, 8)) 57 58 /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */ 59 #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8)) 60 61 #define TICK_NSEC_HPET (SH_DIV(1000000UL * 1000, ACTHZ_HPET, 8)) 62 63 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */ 64 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ) 65 66 /* TICK_USEC_TO_NSEC is the time between ticks in nsec assuming real ACTHZ and */ 67 /* a value TUSEC for TICK_USEC (can be set bij adjtimex) */ 68 #define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8)) 69 70 /* some arch's have a small-data section that can be accessed register-relative 71 * but that can only take up to, say, 4-byte variables. jiffies being part of 72 * an 8-byte variable may not be correctly accessed unless we force the issue 73 */ 74 #define __jiffy_data __attribute__((section(".data"))) 75 76 /* 77 * The 64-bit value is not volatile - you MUST NOT read it 78 * without sampling the sequence number in xtime_lock. 79 * get_jiffies_64() will do this for you as appropriate. 80 */ 81 extern u64 __jiffy_data jiffies_64; 82 extern unsigned long volatile __jiffy_data jiffies; 83 84 #if (BITS_PER_LONG < 64) 85 u64 get_jiffies_64(void); 86 #else 87 static inline u64 get_jiffies_64(void) 88 { 89 return (u64)jiffies; 90 } 91 #endif 92 93 /* 94 * These inlines deal with timer wrapping correctly. You are 95 * strongly encouraged to use them 96 * 1. Because people otherwise forget 97 * 2. Because if the timer wrap changes in future you won't have to 98 * alter your driver code. 99 * 100 * time_after(a,b) returns true if the time a is after time b. 101 * 102 * Do this with "<0" and ">=0" to only test the sign of the result. A 103 * good compiler would generate better code (and a really good compiler 104 * wouldn't care). Gcc is currently neither. 105 */ 106 #define time_after(a,b) \ 107 (typecheck(unsigned long, a) && \ 108 typecheck(unsigned long, b) && \ 109 ((long)(b) - (long)(a) < 0)) 110 #define time_before(a,b) time_after(b,a) 111 112 #define time_after_eq(a,b) \ 113 (typecheck(unsigned long, a) && \ 114 typecheck(unsigned long, b) && \ 115 ((long)(a) - (long)(b) >= 0)) 116 #define time_before_eq(a,b) time_after_eq(b,a) 117 118 /* 119 * Have the 32 bit jiffies value wrap 5 minutes after boot 120 * so jiffies wrap bugs show up earlier. 121 */ 122 #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ)) 123 124 /* 125 * Change timeval to jiffies, trying to avoid the 126 * most obvious overflows.. 127 * 128 * And some not so obvious. 129 * 130 * Note that we don't want to return MAX_LONG, because 131 * for various timeout reasons we often end up having 132 * to wait "jiffies+1" in order to guarantee that we wait 133 * at _least_ "jiffies" - so "jiffies+1" had better still 134 * be positive. 135 */ 136 #define MAX_JIFFY_OFFSET ((~0UL >> 1)-1) 137 138 /* 139 * We want to do realistic conversions of time so we need to use the same 140 * values the update wall clock code uses as the jiffies size. This value 141 * is: TICK_NSEC (which is defined in timex.h). This 142 * is a constant and is in nanoseconds. We will used scaled math 143 * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and 144 * NSEC_JIFFIE_SC. Note that these defines contain nothing but 145 * constants and so are computed at compile time. SHIFT_HZ (computed in 146 * timex.h) adjusts the scaling for different HZ values. 147 148 * Scaled math??? What is that? 149 * 150 * Scaled math is a way to do integer math on values that would, 151 * otherwise, either overflow, underflow, or cause undesired div 152 * instructions to appear in the execution path. In short, we "scale" 153 * up the operands so they take more bits (more precision, less 154 * underflow), do the desired operation and then "scale" the result back 155 * by the same amount. If we do the scaling by shifting we avoid the 156 * costly mpy and the dastardly div instructions. 157 158 * Suppose, for example, we want to convert from seconds to jiffies 159 * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The 160 * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We 161 * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we 162 * might calculate at compile time, however, the result will only have 163 * about 3-4 bits of precision (less for smaller values of HZ). 164 * 165 * So, we scale as follows: 166 * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE); 167 * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE; 168 * Then we make SCALE a power of two so: 169 * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE; 170 * Now we define: 171 * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) 172 * jiff = (sec * SEC_CONV) >> SCALE; 173 * 174 * Often the math we use will expand beyond 32-bits so we tell C how to 175 * do this and pass the 64-bit result of the mpy through the ">> SCALE" 176 * which should take the result back to 32-bits. We want this expansion 177 * to capture as much precision as possible. At the same time we don't 178 * want to overflow so we pick the SCALE to avoid this. In this file, 179 * that means using a different scale for each range of HZ values (as 180 * defined in timex.h). 181 * 182 * For those who want to know, gcc will give a 64-bit result from a "*" 183 * operator if the result is a long long AND at least one of the 184 * operands is cast to long long (usually just prior to the "*" so as 185 * not to confuse it into thinking it really has a 64-bit operand, 186 * which, buy the way, it can do, but it take more code and at least 2 187 * mpys). 188 189 * We also need to be aware that one second in nanoseconds is only a 190 * couple of bits away from overflowing a 32-bit word, so we MUST use 191 * 64-bits to get the full range time in nanoseconds. 192 193 */ 194 195 /* 196 * Here are the scales we will use. One for seconds, nanoseconds and 197 * microseconds. 198 * 199 * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and 200 * check if the sign bit is set. If not, we bump the shift count by 1. 201 * (Gets an extra bit of precision where we can use it.) 202 * We know it is set for HZ = 1024 and HZ = 100 not for 1000. 203 * Haven't tested others. 204 205 * Limits of cpp (for #if expressions) only long (no long long), but 206 * then we only need the most signicant bit. 207 */ 208 209 #define SEC_JIFFIE_SC (31 - SHIFT_HZ) 210 #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000) 211 #undef SEC_JIFFIE_SC 212 #define SEC_JIFFIE_SC (32 - SHIFT_HZ) 213 #endif 214 #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29) 215 #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19) 216 #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\ 217 TICK_NSEC -1) / (u64)TICK_NSEC)) 218 219 #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\ 220 TICK_NSEC -1) / (u64)TICK_NSEC)) 221 #define USEC_CONVERSION \ 222 ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\ 223 TICK_NSEC -1) / (u64)TICK_NSEC)) 224 /* 225 * USEC_ROUND is used in the timeval to jiffie conversion. See there 226 * for more details. It is the scaled resolution rounding value. Note 227 * that it is a 64-bit value. Since, when it is applied, we are already 228 * in jiffies (albit scaled), it is nothing but the bits we will shift 229 * off. 230 */ 231 #define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1) 232 /* 233 * The maximum jiffie value is (MAX_INT >> 1). Here we translate that 234 * into seconds. The 64-bit case will overflow if we are not careful, 235 * so use the messy SH_DIV macro to do it. Still all constants. 236 */ 237 #if BITS_PER_LONG < 64 238 # define MAX_SEC_IN_JIFFIES \ 239 (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC) 240 #else /* take care of overflow on 64 bits machines */ 241 # define MAX_SEC_IN_JIFFIES \ 242 (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1) 243 244 #endif 245 246 /* 247 * Convert jiffies to milliseconds and back. 248 * 249 * Avoid unnecessary multiplications/divisions in the 250 * two most common HZ cases: 251 */ 252 static inline unsigned int jiffies_to_msecs(const unsigned long j) 253 { 254 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) 255 return (MSEC_PER_SEC / HZ) * j; 256 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) 257 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); 258 #else 259 return (j * MSEC_PER_SEC) / HZ; 260 #endif 261 } 262 263 static inline unsigned int jiffies_to_usecs(const unsigned long j) 264 { 265 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) 266 return (USEC_PER_SEC / HZ) * j; 267 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) 268 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC); 269 #else 270 return (j * USEC_PER_SEC) / HZ; 271 #endif 272 } 273 274 static inline unsigned long msecs_to_jiffies(const unsigned int m) 275 { 276 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET)) 277 return MAX_JIFFY_OFFSET; 278 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) 279 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ); 280 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) 281 return m * (HZ / MSEC_PER_SEC); 282 #else 283 return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC; 284 #endif 285 } 286 287 static inline unsigned long usecs_to_jiffies(const unsigned int u) 288 { 289 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET)) 290 return MAX_JIFFY_OFFSET; 291 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) 292 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ); 293 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) 294 return u * (HZ / USEC_PER_SEC); 295 #else 296 return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC; 297 #endif 298 } 299 300 /* 301 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note 302 * that a remainder subtract here would not do the right thing as the 303 * resolution values don't fall on second boundries. I.e. the line: 304 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding. 305 * 306 * Rather, we just shift the bits off the right. 307 * 308 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec 309 * value to a scaled second value. 310 */ 311 static __inline__ unsigned long 312 timespec_to_jiffies(const struct timespec *value) 313 { 314 unsigned long sec = value->tv_sec; 315 long nsec = value->tv_nsec + TICK_NSEC - 1; 316 317 if (sec >= MAX_SEC_IN_JIFFIES){ 318 sec = MAX_SEC_IN_JIFFIES; 319 nsec = 0; 320 } 321 return (((u64)sec * SEC_CONVERSION) + 322 (((u64)nsec * NSEC_CONVERSION) >> 323 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; 324 325 } 326 327 static __inline__ void 328 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value) 329 { 330 /* 331 * Convert jiffies to nanoseconds and separate with 332 * one divide. 333 */ 334 u64 nsec = (u64)jiffies * TICK_NSEC; 335 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec); 336 } 337 338 /* Same for "timeval" 339 * 340 * Well, almost. The problem here is that the real system resolution is 341 * in nanoseconds and the value being converted is in micro seconds. 342 * Also for some machines (those that use HZ = 1024, in-particular), 343 * there is a LARGE error in the tick size in microseconds. 344 345 * The solution we use is to do the rounding AFTER we convert the 346 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off. 347 * Instruction wise, this should cost only an additional add with carry 348 * instruction above the way it was done above. 349 */ 350 static __inline__ unsigned long 351 timeval_to_jiffies(const struct timeval *value) 352 { 353 unsigned long sec = value->tv_sec; 354 long usec = value->tv_usec; 355 356 if (sec >= MAX_SEC_IN_JIFFIES){ 357 sec = MAX_SEC_IN_JIFFIES; 358 usec = 0; 359 } 360 return (((u64)sec * SEC_CONVERSION) + 361 (((u64)usec * USEC_CONVERSION + USEC_ROUND) >> 362 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; 363 } 364 365 static __inline__ void 366 jiffies_to_timeval(const unsigned long jiffies, struct timeval *value) 367 { 368 /* 369 * Convert jiffies to nanoseconds and separate with 370 * one divide. 371 */ 372 u64 nsec = (u64)jiffies * TICK_NSEC; 373 long tv_usec; 374 375 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tv_usec); 376 tv_usec /= NSEC_PER_USEC; 377 value->tv_usec = tv_usec; 378 } 379 380 /* 381 * Convert jiffies/jiffies_64 to clock_t and back. 382 */ 383 static inline clock_t jiffies_to_clock_t(long x) 384 { 385 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 386 return x / (HZ / USER_HZ); 387 #else 388 u64 tmp = (u64)x * TICK_NSEC; 389 do_div(tmp, (NSEC_PER_SEC / USER_HZ)); 390 return (long)tmp; 391 #endif 392 } 393 394 static inline unsigned long clock_t_to_jiffies(unsigned long x) 395 { 396 #if (HZ % USER_HZ)==0 397 if (x >= ~0UL / (HZ / USER_HZ)) 398 return ~0UL; 399 return x * (HZ / USER_HZ); 400 #else 401 u64 jif; 402 403 /* Don't worry about loss of precision here .. */ 404 if (x >= ~0UL / HZ * USER_HZ) 405 return ~0UL; 406 407 /* .. but do try to contain it here */ 408 jif = x * (u64) HZ; 409 do_div(jif, USER_HZ); 410 return jif; 411 #endif 412 } 413 414 static inline u64 jiffies_64_to_clock_t(u64 x) 415 { 416 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 417 do_div(x, HZ / USER_HZ); 418 #else 419 /* 420 * There are better ways that don't overflow early, 421 * but even this doesn't overflow in hundreds of years 422 * in 64 bits, so.. 423 */ 424 x *= TICK_NSEC; 425 do_div(x, (NSEC_PER_SEC / USER_HZ)); 426 #endif 427 return x; 428 } 429 430 static inline u64 nsec_to_clock_t(u64 x) 431 { 432 #if (NSEC_PER_SEC % USER_HZ) == 0 433 do_div(x, (NSEC_PER_SEC / USER_HZ)); 434 #elif (USER_HZ % 512) == 0 435 x *= USER_HZ/512; 436 do_div(x, (NSEC_PER_SEC / 512)); 437 #else 438 /* 439 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024, 440 * overflow after 64.99 years. 441 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ... 442 */ 443 x *= 9; 444 do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2)) 445 / USER_HZ)); 446 #endif 447 return x; 448 } 449 450 #endif 451
