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