include/linux/jiffies.h

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