jiffies.h 11 KB

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  1. #ifndef _LINUX_JIFFIES_H
  2. #define _LINUX_JIFFIES_H
  3. #include <linux/calc64.h>
  4. #include <linux/kernel.h>
  5. #include <linux/types.h>
  6. #include <linux/time.h>
  7. #include <linux/timex.h>
  8. #include <asm/param.h> /* for HZ */
  9. /*
  10. * The following defines establish the engineering parameters of the PLL
  11. * model. The HZ variable establishes the timer interrupt frequency, 100 Hz
  12. * for the SunOS kernel, 256 Hz for the Ultrix kernel and 1024 Hz for the
  13. * OSF/1 kernel. The SHIFT_HZ define expresses the same value as the
  14. * nearest power of two in order to avoid hardware multiply operations.
  15. */
  16. #if HZ >= 12 && HZ < 24
  17. # define SHIFT_HZ 4
  18. #elif HZ >= 24 && HZ < 48
  19. # define SHIFT_HZ 5
  20. #elif HZ >= 48 && HZ < 96
  21. # define SHIFT_HZ 6
  22. #elif HZ >= 96 && HZ < 192
  23. # define SHIFT_HZ 7
  24. #elif HZ >= 192 && HZ < 384
  25. # define SHIFT_HZ 8
  26. #elif HZ >= 384 && HZ < 768
  27. # define SHIFT_HZ 9
  28. #elif HZ >= 768 && HZ < 1536
  29. # define SHIFT_HZ 10
  30. #else
  31. # error You lose.
  32. #endif
  33. /* LATCH is used in the interval timer and ftape setup. */
  34. #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */
  35. #define LATCH_HPET ((HPET_TICK_RATE + HZ/2) / HZ)
  36. /* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, the we can
  37. * improve accuracy by shifting LSH bits, hence calculating:
  38. * (NOM << LSH) / DEN
  39. * This however means trouble for large NOM, because (NOM << LSH) may no
  40. * longer fit in 32 bits. The following way of calculating this gives us
  41. * some slack, under the following conditions:
  42. * - (NOM / DEN) fits in (32 - LSH) bits.
  43. * - (NOM % DEN) fits in (32 - LSH) bits.
  44. */
  45. #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \
  46. + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
  47. /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
  48. #define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
  49. #define ACTHZ_HPET (SH_DIV (HPET_TICK_RATE, LATCH_HPET, 8))
  50. /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */
  51. #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8))
  52. #define TICK_NSEC_HPET (SH_DIV(1000000UL * 1000, ACTHZ_HPET, 8))
  53. /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
  54. #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
  55. /* TICK_USEC_TO_NSEC is the time between ticks in nsec assuming real ACTHZ and */
  56. /* a value TUSEC for TICK_USEC (can be set bij adjtimex) */
  57. #define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8))
  58. /* some arch's have a small-data section that can be accessed register-relative
  59. * but that can only take up to, say, 4-byte variables. jiffies being part of
  60. * an 8-byte variable may not be correctly accessed unless we force the issue
  61. */
  62. #define __jiffy_data __attribute__((section(".data")))
  63. /*
  64. * The 64-bit value is not atomic - you MUST NOT read it
  65. * without sampling the sequence number in xtime_lock.
  66. * get_jiffies_64() will do this for you as appropriate.
  67. */
  68. extern u64 __jiffy_data jiffies_64;
  69. extern unsigned long volatile __jiffy_data jiffies;
  70. #if (BITS_PER_LONG < 64)
  71. u64 get_jiffies_64(void);
  72. #else
  73. static inline u64 get_jiffies_64(void)
  74. {
  75. return (u64)jiffies;
  76. }
  77. #endif
  78. /*
  79. * These inlines deal with timer wrapping correctly. You are
  80. * strongly encouraged to use them
  81. * 1. Because people otherwise forget
  82. * 2. Because if the timer wrap changes in future you won't have to
  83. * alter your driver code.
  84. *
  85. * time_after(a,b) returns true if the time a is after time b.
  86. *
  87. * Do this with "<0" and ">=0" to only test the sign of the result. A
  88. * good compiler would generate better code (and a really good compiler
  89. * wouldn't care). Gcc is currently neither.
  90. */
  91. #define time_after(a,b) \
  92. (typecheck(unsigned long, a) && \
  93. typecheck(unsigned long, b) && \
  94. ((long)(b) - (long)(a) < 0))
  95. #define time_before(a,b) time_after(b,a)
  96. #define time_after_eq(a,b) \
  97. (typecheck(unsigned long, a) && \
  98. typecheck(unsigned long, b) && \
  99. ((long)(a) - (long)(b) >= 0))
  100. #define time_before_eq(a,b) time_after_eq(b,a)
  101. /* Same as above, but does so with platform independent 64bit types.
  102. * These must be used when utilizing jiffies_64 (i.e. return value of
  103. * get_jiffies_64() */
  104. #define time_after64(a,b) \
  105. (typecheck(__u64, a) && \
  106. typecheck(__u64, b) && \
  107. ((__s64)(b) - (__s64)(a) < 0))
  108. #define time_before64(a,b) time_after64(b,a)
  109. #define time_after_eq64(a,b) \
  110. (typecheck(__u64, a) && \
  111. typecheck(__u64, b) && \
  112. ((__s64)(a) - (__s64)(b) >= 0))
  113. #define time_before_eq64(a,b) time_after_eq64(b,a)
  114. /*
  115. * Have the 32 bit jiffies value wrap 5 minutes after boot
  116. * so jiffies wrap bugs show up earlier.
  117. */
  118. #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
  119. /*
  120. * Change timeval to jiffies, trying to avoid the
  121. * most obvious overflows..
  122. *
  123. * And some not so obvious.
  124. *
  125. * Note that we don't want to return LONG_MAX, because
  126. * for various timeout reasons we often end up having
  127. * to wait "jiffies+1" in order to guarantee that we wait
  128. * at _least_ "jiffies" - so "jiffies+1" had better still
  129. * be positive.
  130. */
  131. #define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1)
  132. /*
  133. * We want to do realistic conversions of time so we need to use the same
  134. * values the update wall clock code uses as the jiffies size. This value
  135. * is: TICK_NSEC (which is defined in timex.h). This
  136. * is a constant and is in nanoseconds. We will used scaled math
  137. * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and
  138. * NSEC_JIFFIE_SC. Note that these defines contain nothing but
  139. * constants and so are computed at compile time. SHIFT_HZ (computed in
  140. * timex.h) adjusts the scaling for different HZ values.
  141. * Scaled math??? What is that?
  142. *
  143. * Scaled math is a way to do integer math on values that would,
  144. * otherwise, either overflow, underflow, or cause undesired div
  145. * instructions to appear in the execution path. In short, we "scale"
  146. * up the operands so they take more bits (more precision, less
  147. * underflow), do the desired operation and then "scale" the result back
  148. * by the same amount. If we do the scaling by shifting we avoid the
  149. * costly mpy and the dastardly div instructions.
  150. * Suppose, for example, we want to convert from seconds to jiffies
  151. * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The
  152. * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
  153. * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
  154. * might calculate at compile time, however, the result will only have
  155. * about 3-4 bits of precision (less for smaller values of HZ).
  156. *
  157. * So, we scale as follows:
  158. * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
  159. * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
  160. * Then we make SCALE a power of two so:
  161. * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
  162. * Now we define:
  163. * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
  164. * jiff = (sec * SEC_CONV) >> SCALE;
  165. *
  166. * Often the math we use will expand beyond 32-bits so we tell C how to
  167. * do this and pass the 64-bit result of the mpy through the ">> SCALE"
  168. * which should take the result back to 32-bits. We want this expansion
  169. * to capture as much precision as possible. At the same time we don't
  170. * want to overflow so we pick the SCALE to avoid this. In this file,
  171. * that means using a different scale for each range of HZ values (as
  172. * defined in timex.h).
  173. *
  174. * For those who want to know, gcc will give a 64-bit result from a "*"
  175. * operator if the result is a long long AND at least one of the
  176. * operands is cast to long long (usually just prior to the "*" so as
  177. * not to confuse it into thinking it really has a 64-bit operand,
  178. * which, buy the way, it can do, but it take more code and at least 2
  179. * mpys).
  180. * We also need to be aware that one second in nanoseconds is only a
  181. * couple of bits away from overflowing a 32-bit word, so we MUST use
  182. * 64-bits to get the full range time in nanoseconds.
  183. */
  184. /*
  185. * Here are the scales we will use. One for seconds, nanoseconds and
  186. * microseconds.
  187. *
  188. * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
  189. * check if the sign bit is set. If not, we bump the shift count by 1.
  190. * (Gets an extra bit of precision where we can use it.)
  191. * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
  192. * Haven't tested others.
  193. * Limits of cpp (for #if expressions) only long (no long long), but
  194. * then we only need the most signicant bit.
  195. */
  196. #define SEC_JIFFIE_SC (31 - SHIFT_HZ)
  197. #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
  198. #undef SEC_JIFFIE_SC
  199. #define SEC_JIFFIE_SC (32 - SHIFT_HZ)
  200. #endif
  201. #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
  202. #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
  203. #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
  204. TICK_NSEC -1) / (u64)TICK_NSEC))
  205. #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
  206. TICK_NSEC -1) / (u64)TICK_NSEC))
  207. #define USEC_CONVERSION \
  208. ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
  209. TICK_NSEC -1) / (u64)TICK_NSEC))
  210. /*
  211. * USEC_ROUND is used in the timeval to jiffie conversion. See there
  212. * for more details. It is the scaled resolution rounding value. Note
  213. * that it is a 64-bit value. Since, when it is applied, we are already
  214. * in jiffies (albit scaled), it is nothing but the bits we will shift
  215. * off.
  216. */
  217. #define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
  218. /*
  219. * The maximum jiffie value is (MAX_INT >> 1). Here we translate that
  220. * into seconds. The 64-bit case will overflow if we are not careful,
  221. * so use the messy SH_DIV macro to do it. Still all constants.
  222. */
  223. #if BITS_PER_LONG < 64
  224. # define MAX_SEC_IN_JIFFIES \
  225. (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
  226. #else /* take care of overflow on 64 bits machines */
  227. # define MAX_SEC_IN_JIFFIES \
  228. (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
  229. #endif
  230. /*
  231. * Convert various time units to each other:
  232. */
  233. extern unsigned int jiffies_to_msecs(const unsigned long j);
  234. extern unsigned int jiffies_to_usecs(const unsigned long j);
  235. extern unsigned long msecs_to_jiffies(const unsigned int m);
  236. extern unsigned long usecs_to_jiffies(const unsigned int u);
  237. extern unsigned long timespec_to_jiffies(const struct timespec *value);
  238. extern void jiffies_to_timespec(const unsigned long jiffies,
  239. struct timespec *value);
  240. extern unsigned long timeval_to_jiffies(const struct timeval *value);
  241. extern void jiffies_to_timeval(const unsigned long jiffies,
  242. struct timeval *value);
  243. extern clock_t jiffies_to_clock_t(long x);
  244. extern unsigned long clock_t_to_jiffies(unsigned long x);
  245. extern u64 jiffies_64_to_clock_t(u64 x);
  246. extern u64 nsec_to_clock_t(u64 x);
  247. #define TIMESTAMP_SIZE 30
  248. #endif