blob: 99905e180532e094c2efb0fc8c3ce6c66c63d92b [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001#ifndef _LINUX_JIFFIES_H
2#define _LINUX_JIFFIES_H
3
Thomas Gleixner5cca7612006-01-09 20:52:20 -08004#include <linux/calc64.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07005#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 */
Linus Torvalds1da177e2005-04-16 15:20:36 -070010
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 volatile - 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 */
75extern u64 __jiffy_data jiffies_64;
76extern unsigned long volatile __jiffy_data jiffies;
77
78#if (BITS_PER_LONG < 64)
79u64 get_jiffies_64(void);
80#else
81static 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/*
113 * Have the 32 bit jiffies value wrap 5 minutes after boot
114 * so jiffies wrap bugs show up earlier.
115 */
116#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
117
118/*
119 * Change timeval to jiffies, trying to avoid the
120 * most obvious overflows..
121 *
122 * And some not so obvious.
123 *
124 * Note that we don't want to return MAX_LONG, because
125 * for various timeout reasons we often end up having
126 * to wait "jiffies+1" in order to guarantee that we wait
127 * at _least_ "jiffies" - so "jiffies+1" had better still
128 * be positive.
129 */
130#define MAX_JIFFY_OFFSET ((~0UL >> 1)-1)
131
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
142 * Scaled math??? What is that?
143 *
144 * Scaled math is a way to do integer math on values that would,
145 * otherwise, either overflow, underflow, or cause undesired div
146 * instructions to appear in the execution path. In short, we "scale"
147 * up the operands so they take more bits (more precision, less
148 * underflow), do the desired operation and then "scale" the result back
149 * by the same amount. If we do the scaling by shifting we avoid the
150 * costly mpy and the dastardly div instructions.
151
152 * Suppose, for example, we want to convert from seconds to jiffies
153 * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The
154 * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
155 * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
156 * might calculate at compile time, however, the result will only have
157 * about 3-4 bits of precision (less for smaller values of HZ).
158 *
159 * So, we scale as follows:
160 * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
161 * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
162 * Then we make SCALE a power of two so:
163 * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
164 * Now we define:
165 * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
166 * jiff = (sec * SEC_CONV) >> SCALE;
167 *
168 * Often the math we use will expand beyond 32-bits so we tell C how to
169 * do this and pass the 64-bit result of the mpy through the ">> SCALE"
170 * which should take the result back to 32-bits. We want this expansion
171 * to capture as much precision as possible. At the same time we don't
172 * want to overflow so we pick the SCALE to avoid this. In this file,
173 * that means using a different scale for each range of HZ values (as
174 * defined in timex.h).
175 *
176 * For those who want to know, gcc will give a 64-bit result from a "*"
177 * operator if the result is a long long AND at least one of the
178 * operands is cast to long long (usually just prior to the "*" so as
179 * not to confuse it into thinking it really has a 64-bit operand,
180 * which, buy the way, it can do, but it take more code and at least 2
181 * mpys).
182
183 * We also need to be aware that one second in nanoseconds is only a
184 * couple of bits away from overflowing a 32-bit word, so we MUST use
185 * 64-bits to get the full range time in nanoseconds.
186
187 */
188
189/*
190 * Here are the scales we will use. One for seconds, nanoseconds and
191 * microseconds.
192 *
193 * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
194 * check if the sign bit is set. If not, we bump the shift count by 1.
195 * (Gets an extra bit of precision where we can use it.)
196 * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
197 * Haven't tested others.
198
199 * Limits of cpp (for #if expressions) only long (no long long), but
200 * then we only need the most signicant bit.
201 */
202
203#define SEC_JIFFIE_SC (31 - SHIFT_HZ)
204#if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
205#undef SEC_JIFFIE_SC
206#define SEC_JIFFIE_SC (32 - SHIFT_HZ)
207#endif
208#define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
209#define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
210#define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
211 TICK_NSEC -1) / (u64)TICK_NSEC))
212
213#define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
214 TICK_NSEC -1) / (u64)TICK_NSEC))
215#define USEC_CONVERSION \
216 ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
217 TICK_NSEC -1) / (u64)TICK_NSEC))
218/*
219 * USEC_ROUND is used in the timeval to jiffie conversion. See there
220 * for more details. It is the scaled resolution rounding value. Note
221 * that it is a 64-bit value. Since, when it is applied, we are already
222 * in jiffies (albit scaled), it is nothing but the bits we will shift
223 * off.
224 */
225#define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
226/*
227 * The maximum jiffie value is (MAX_INT >> 1). Here we translate that
228 * into seconds. The 64-bit case will overflow if we are not careful,
229 * so use the messy SH_DIV macro to do it. Still all constants.
230 */
231#if BITS_PER_LONG < 64
232# define MAX_SEC_IN_JIFFIES \
233 (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
234#else /* take care of overflow on 64 bits machines */
235# define MAX_SEC_IN_JIFFIES \
236 (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
237
238#endif
239
240/*
241 * Convert jiffies to milliseconds and back.
242 *
243 * Avoid unnecessary multiplications/divisions in the
244 * two most common HZ cases:
245 */
246static inline unsigned int jiffies_to_msecs(const unsigned long j)
247{
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700248#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
249 return (MSEC_PER_SEC / HZ) * j;
250#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
251 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700252#else
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700253 return (j * MSEC_PER_SEC) / HZ;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700254#endif
255}
256
257static inline unsigned int jiffies_to_usecs(const unsigned long j)
258{
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700259#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
260 return (USEC_PER_SEC / HZ) * j;
261#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
262 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700263#else
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700264 return (j * USEC_PER_SEC) / HZ;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700265#endif
266}
267
268static inline unsigned long msecs_to_jiffies(const unsigned int m)
269{
270 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
271 return MAX_JIFFY_OFFSET;
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700272#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
273 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
274#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
275 return m * (HZ / MSEC_PER_SEC);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700276#else
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700277 return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700278#endif
279}
280
281static inline unsigned long usecs_to_jiffies(const unsigned int u)
282{
283 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
284 return MAX_JIFFY_OFFSET;
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700285#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
286 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
287#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
288 return u * (HZ / USEC_PER_SEC);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700289#else
Nishanth Aravamudan84f902c2005-09-10 00:27:22 -0700290 return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700291#endif
292}
293
294/*
295 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
296 * that a remainder subtract here would not do the right thing as the
297 * resolution values don't fall on second boundries. I.e. the line:
298 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
299 *
300 * Rather, we just shift the bits off the right.
301 *
302 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
303 * value to a scaled second value.
304 */
305static __inline__ unsigned long
306timespec_to_jiffies(const struct timespec *value)
307{
308 unsigned long sec = value->tv_sec;
309 long nsec = value->tv_nsec + TICK_NSEC - 1;
310
311 if (sec >= MAX_SEC_IN_JIFFIES){
312 sec = MAX_SEC_IN_JIFFIES;
313 nsec = 0;
314 }
315 return (((u64)sec * SEC_CONVERSION) +
316 (((u64)nsec * NSEC_CONVERSION) >>
317 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
318
319}
320
321static __inline__ void
322jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
323{
324 /*
325 * Convert jiffies to nanoseconds and separate with
326 * one divide.
327 */
328 u64 nsec = (u64)jiffies * TICK_NSEC;
329 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec);
330}
331
332/* Same for "timeval"
333 *
334 * Well, almost. The problem here is that the real system resolution is
335 * in nanoseconds and the value being converted is in micro seconds.
336 * Also for some machines (those that use HZ = 1024, in-particular),
337 * there is a LARGE error in the tick size in microseconds.
338
339 * The solution we use is to do the rounding AFTER we convert the
340 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
341 * Instruction wise, this should cost only an additional add with carry
342 * instruction above the way it was done above.
343 */
344static __inline__ unsigned long
345timeval_to_jiffies(const struct timeval *value)
346{
347 unsigned long sec = value->tv_sec;
348 long usec = value->tv_usec;
349
350 if (sec >= MAX_SEC_IN_JIFFIES){
351 sec = MAX_SEC_IN_JIFFIES;
352 usec = 0;
353 }
354 return (((u64)sec * SEC_CONVERSION) +
355 (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
356 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
357}
358
359static __inline__ void
360jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
361{
362 /*
363 * Convert jiffies to nanoseconds and separate with
364 * one divide.
365 */
366 u64 nsec = (u64)jiffies * TICK_NSEC;
Thomas Gleixner5cca7612006-01-09 20:52:20 -0800367 long tv_usec;
368
369 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tv_usec);
370 tv_usec /= NSEC_PER_USEC;
371 value->tv_usec = tv_usec;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700372}
373
374/*
375 * Convert jiffies/jiffies_64 to clock_t and back.
376 */
377static inline clock_t jiffies_to_clock_t(long x)
378{
379#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
380 return x / (HZ / USER_HZ);
381#else
382 u64 tmp = (u64)x * TICK_NSEC;
383 do_div(tmp, (NSEC_PER_SEC / USER_HZ));
384 return (long)tmp;
385#endif
386}
387
388static inline unsigned long clock_t_to_jiffies(unsigned long x)
389{
390#if (HZ % USER_HZ)==0
391 if (x >= ~0UL / (HZ / USER_HZ))
392 return ~0UL;
393 return x * (HZ / USER_HZ);
394#else
395 u64 jif;
396
397 /* Don't worry about loss of precision here .. */
398 if (x >= ~0UL / HZ * USER_HZ)
399 return ~0UL;
400
401 /* .. but do try to contain it here */
402 jif = x * (u64) HZ;
403 do_div(jif, USER_HZ);
404 return jif;
405#endif
406}
407
408static inline u64 jiffies_64_to_clock_t(u64 x)
409{
410#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
411 do_div(x, HZ / USER_HZ);
412#else
413 /*
414 * There are better ways that don't overflow early,
415 * but even this doesn't overflow in hundreds of years
416 * in 64 bits, so..
417 */
418 x *= TICK_NSEC;
419 do_div(x, (NSEC_PER_SEC / USER_HZ));
420#endif
421 return x;
422}
423
424static inline u64 nsec_to_clock_t(u64 x)
425{
426#if (NSEC_PER_SEC % USER_HZ) == 0
427 do_div(x, (NSEC_PER_SEC / USER_HZ));
428#elif (USER_HZ % 512) == 0
429 x *= USER_HZ/512;
430 do_div(x, (NSEC_PER_SEC / 512));
431#else
432 /*
433 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
434 * overflow after 64.99 years.
435 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
436 */
437 x *= 9;
438 do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2))
439 / USER_HZ));
440#endif
441 return x;
442}
443
444#endif