linux/include/linux/jiffies.h
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   1#ifndef _LINUX_JIFFIES_H
   2#define _LINUX_JIFFIES_H
   3
   4#include <linux/math64.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#elif HZ >= 1536 && HZ < 3072
  33# define SHIFT_HZ       11
  34#elif HZ >= 3072 && HZ < 6144
  35# define SHIFT_HZ       12
  36#elif HZ >= 6144 && HZ < 12288
  37# define SHIFT_HZ       13
  38#else
  39# error Invalid value of HZ.
  40#endif
  41
  42/* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
  43 * improve accuracy by shifting LSH bits, hence calculating:
  44 *     (NOM << LSH) / DEN
  45 * This however means trouble for large NOM, because (NOM << LSH) may no
  46 * longer fit in 32 bits. The following way of calculating this gives us
  47 * some slack, under the following conditions:
  48 *   - (NOM / DEN) fits in (32 - LSH) bits.
  49 *   - (NOM % DEN) fits in (32 - LSH) bits.
  50 */
  51#define SH_DIV(NOM,DEN,LSH) (   (((NOM) / (DEN)) << (LSH))              \
  52                             + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
  53
  54#ifdef CLOCK_TICK_RATE
  55/* LATCH is used in the interval timer and ftape setup. */
  56# define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)  /* For divider */
  57
  58/*
  59 * HZ is the requested value. However the CLOCK_TICK_RATE may not allow
  60 * for exactly HZ. So SHIFTED_HZ is high res HZ ("<< 8" is for accuracy)
  61 */
  62# define SHIFTED_HZ (SH_DIV(CLOCK_TICK_RATE, LATCH, 8))
  63#else
  64# define SHIFTED_HZ (HZ << 8)
  65#endif
  66
  67/* TICK_NSEC is the time between ticks in nsec assuming SHIFTED_HZ */
  68#define TICK_NSEC (SH_DIV(1000000UL * 1000, SHIFTED_HZ, 8))
  69
  70/* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
  71#define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
  72
  73/*
  74 * TICK_USEC_TO_NSEC is the time between ticks in nsec assuming SHIFTED_HZ and
  75 * a value TUSEC for TICK_USEC (can be set bij adjtimex)
  76 */
  77#define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV(TUSEC * USER_HZ * 1000, SHIFTED_HZ, 8))
  78
  79/* some arch's have a small-data section that can be accessed register-relative
  80 * but that can only take up to, say, 4-byte variables. jiffies being part of
  81 * an 8-byte variable may not be correctly accessed unless we force the issue
  82 */
  83#define __jiffy_data  __attribute__((section(".data")))
  84
  85/*
  86 * The 64-bit value is not atomic - you MUST NOT read it
  87 * without sampling the sequence number in xtime_lock.
  88 * get_jiffies_64() will do this for you as appropriate.
  89 */
  90extern u64 __jiffy_data jiffies_64;
  91extern unsigned long volatile __jiffy_data jiffies;
  92
  93#if (BITS_PER_LONG < 64)
  94u64 get_jiffies_64(void);
  95#else
  96static inline u64 get_jiffies_64(void)
  97{
  98        return (u64)jiffies;
  99}
 100#endif
 101
 102/*
 103 *      These inlines deal with timer wrapping correctly. You are 
 104 *      strongly encouraged to use them
 105 *      1. Because people otherwise forget
 106 *      2. Because if the timer wrap changes in future you won't have to
 107 *         alter your driver code.
 108 *
 109 * time_after(a,b) returns true if the time a is after time b.
 110 *
 111 * Do this with "<0" and ">=0" to only test the sign of the result. A
 112 * good compiler would generate better code (and a really good compiler
 113 * wouldn't care). Gcc is currently neither.
 114 */
 115#define time_after(a,b)         \
 116        (typecheck(unsigned long, a) && \
 117         typecheck(unsigned long, b) && \
 118         ((long)(b) - (long)(a) < 0))
 119#define time_before(a,b)        time_after(b,a)
 120
 121#define time_after_eq(a,b)      \
 122        (typecheck(unsigned long, a) && \
 123         typecheck(unsigned long, b) && \
 124         ((long)(a) - (long)(b) >= 0))
 125#define time_before_eq(a,b)     time_after_eq(b,a)
 126
 127/*
 128 * Calculate whether a is in the range of [b, c].
 129 */
 130#define time_in_range(a,b,c) \
 131        (time_after_eq(a,b) && \
 132         time_before_eq(a,c))
 133
 134/*
 135 * Calculate whether a is in the range of [b, c).
 136 */
 137#define time_in_range_open(a,b,c) \
 138        (time_after_eq(a,b) && \
 139         time_before(a,c))
 140
 141/* Same as above, but does so with platform independent 64bit types.
 142 * These must be used when utilizing jiffies_64 (i.e. return value of
 143 * get_jiffies_64() */
 144#define time_after64(a,b)       \
 145        (typecheck(__u64, a) && \
 146         typecheck(__u64, b) && \
 147         ((__s64)(b) - (__s64)(a) < 0))
 148#define time_before64(a,b)      time_after64(b,a)
 149
 150#define time_after_eq64(a,b)    \
 151        (typecheck(__u64, a) && \
 152         typecheck(__u64, b) && \
 153         ((__s64)(a) - (__s64)(b) >= 0))
 154#define time_before_eq64(a,b)   time_after_eq64(b,a)
 155
 156/*
 157 * These four macros compare jiffies and 'a' for convenience.
 158 */
 159
 160/* time_is_before_jiffies(a) return true if a is before jiffies */
 161#define time_is_before_jiffies(a) time_after(jiffies, a)
 162
 163/* time_is_after_jiffies(a) return true if a is after jiffies */
 164#define time_is_after_jiffies(a) time_before(jiffies, a)
 165
 166/* time_is_before_eq_jiffies(a) return true if a is before or equal to jiffies*/
 167#define time_is_before_eq_jiffies(a) time_after_eq(jiffies, a)
 168
 169/* time_is_after_eq_jiffies(a) return true if a is after or equal to jiffies*/
 170#define time_is_after_eq_jiffies(a) time_before_eq(jiffies, a)
 171
 172/*
 173 * Have the 32 bit jiffies value wrap 5 minutes after boot
 174 * so jiffies wrap bugs show up earlier.
 175 */
 176#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
 177
 178/*
 179 * Change timeval to jiffies, trying to avoid the
 180 * most obvious overflows..
 181 *
 182 * And some not so obvious.
 183 *
 184 * Note that we don't want to return LONG_MAX, because
 185 * for various timeout reasons we often end up having
 186 * to wait "jiffies+1" in order to guarantee that we wait
 187 * at _least_ "jiffies" - so "jiffies+1" had better still
 188 * be positive.
 189 */
 190#define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1)
 191
 192extern unsigned long preset_lpj;
 193
 194/*
 195 * We want to do realistic conversions of time so we need to use the same
 196 * values the update wall clock code uses as the jiffies size.  This value
 197 * is: TICK_NSEC (which is defined in timex.h).  This
 198 * is a constant and is in nanoseconds.  We will use scaled math
 199 * with a set of scales defined here as SEC_JIFFIE_SC,  USEC_JIFFIE_SC and
 200 * NSEC_JIFFIE_SC.  Note that these defines contain nothing but
 201 * constants and so are computed at compile time.  SHIFT_HZ (computed in
 202 * timex.h) adjusts the scaling for different HZ values.
 203
 204 * Scaled math???  What is that?
 205 *
 206 * Scaled math is a way to do integer math on values that would,
 207 * otherwise, either overflow, underflow, or cause undesired div
 208 * instructions to appear in the execution path.  In short, we "scale"
 209 * up the operands so they take more bits (more precision, less
 210 * underflow), do the desired operation and then "scale" the result back
 211 * by the same amount.  If we do the scaling by shifting we avoid the
 212 * costly mpy and the dastardly div instructions.
 213
 214 * Suppose, for example, we want to convert from seconds to jiffies
 215 * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE.  The
 216 * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
 217 * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
 218 * might calculate at compile time, however, the result will only have
 219 * about 3-4 bits of precision (less for smaller values of HZ).
 220 *
 221 * So, we scale as follows:
 222 * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
 223 * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
 224 * Then we make SCALE a power of two so:
 225 * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
 226 * Now we define:
 227 * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
 228 * jiff = (sec * SEC_CONV) >> SCALE;
 229 *
 230 * Often the math we use will expand beyond 32-bits so we tell C how to
 231 * do this and pass the 64-bit result of the mpy through the ">> SCALE"
 232 * which should take the result back to 32-bits.  We want this expansion
 233 * to capture as much precision as possible.  At the same time we don't
 234 * want to overflow so we pick the SCALE to avoid this.  In this file,
 235 * that means using a different scale for each range of HZ values (as
 236 * defined in timex.h).
 237 *
 238 * For those who want to know, gcc will give a 64-bit result from a "*"
 239 * operator if the result is a long long AND at least one of the
 240 * operands is cast to long long (usually just prior to the "*" so as
 241 * not to confuse it into thinking it really has a 64-bit operand,
 242 * which, buy the way, it can do, but it takes more code and at least 2
 243 * mpys).
 244
 245 * We also need to be aware that one second in nanoseconds is only a
 246 * couple of bits away from overflowing a 32-bit word, so we MUST use
 247 * 64-bits to get the full range time in nanoseconds.
 248
 249 */
 250
 251/*
 252 * Here are the scales we will use.  One for seconds, nanoseconds and
 253 * microseconds.
 254 *
 255 * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
 256 * check if the sign bit is set.  If not, we bump the shift count by 1.
 257 * (Gets an extra bit of precision where we can use it.)
 258 * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
 259 * Haven't tested others.
 260
 261 * Limits of cpp (for #if expressions) only long (no long long), but
 262 * then we only need the most signicant bit.
 263 */
 264
 265#define SEC_JIFFIE_SC (31 - SHIFT_HZ)
 266#if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
 267#undef SEC_JIFFIE_SC
 268#define SEC_JIFFIE_SC (32 - SHIFT_HZ)
 269#endif
 270#define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
 271#define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
 272#define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
 273                                TICK_NSEC -1) / (u64)TICK_NSEC))
 274
 275#define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
 276                                        TICK_NSEC -1) / (u64)TICK_NSEC))
 277#define USEC_CONVERSION  \
 278                    ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
 279                                        TICK_NSEC -1) / (u64)TICK_NSEC))
 280/*
 281 * USEC_ROUND is used in the timeval to jiffie conversion.  See there
 282 * for more details.  It is the scaled resolution rounding value.  Note
 283 * that it is a 64-bit value.  Since, when it is applied, we are already
 284 * in jiffies (albit scaled), it is nothing but the bits we will shift
 285 * off.
 286 */
 287#define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
 288/*
 289 * The maximum jiffie value is (MAX_INT >> 1).  Here we translate that
 290 * into seconds.  The 64-bit case will overflow if we are not careful,
 291 * so use the messy SH_DIV macro to do it.  Still all constants.
 292 */
 293#if BITS_PER_LONG < 64
 294# define MAX_SEC_IN_JIFFIES \
 295        (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
 296#else   /* take care of overflow on 64 bits machines */
 297# define MAX_SEC_IN_JIFFIES \
 298        (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
 299
 300#endif
 301
 302/*
 303 * Convert various time units to each other:
 304 */
 305extern unsigned int jiffies_to_msecs(const unsigned long j);
 306extern unsigned int jiffies_to_usecs(const unsigned long j);
 307extern unsigned long msecs_to_jiffies(const unsigned int m);
 308extern unsigned long usecs_to_jiffies(const unsigned int u);
 309extern unsigned long timespec_to_jiffies(const struct timespec *value);
 310extern void jiffies_to_timespec(const unsigned long jiffies,
 311                                struct timespec *value);
 312extern unsigned long timeval_to_jiffies(const struct timeval *value);
 313extern void jiffies_to_timeval(const unsigned long jiffies,
 314                               struct timeval *value);
 315extern clock_t jiffies_to_clock_t(unsigned long x);
 316extern unsigned long clock_t_to_jiffies(unsigned long x);
 317extern u64 jiffies_64_to_clock_t(u64 x);
 318extern u64 nsec_to_clock_t(u64 x);
 319extern u64 nsecs_to_jiffies64(u64 n);
 320extern unsigned long nsecs_to_jiffies(u64 n);
 321
 322#define TIMESTAMP_SIZE  30
 323
 324#endif
 325
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