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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /include/linux/jiffies.h
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'include/linux/jiffies.h')
-rw-r--r--include/linux/jiffies.h450
1 files changed, 450 insertions, 0 deletions
diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
new file mode 100644
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1#ifndef _LINUX_JIFFIES_H
2#define _LINUX_JIFFIES_H
3
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#include <asm/div64.h>
10
11#ifndef div_long_long_rem
12#define div_long_long_rem(dividend,divisor,remainder) \
13({ \
14 u64 result = dividend; \
15 *remainder = do_div(result,divisor); \
16 result; \
17})
18#endif
19
20/*
21 * The following defines establish the engineering parameters of the PLL
22 * model. The HZ variable establishes the timer interrupt frequency, 100 Hz
23 * for the SunOS kernel, 256 Hz for the Ultrix kernel and 1024 Hz for the
24 * OSF/1 kernel. The SHIFT_HZ define expresses the same value as the
25 * nearest power of two in order to avoid hardware multiply operations.
26 */
27#if HZ >= 12 && HZ < 24
28# define SHIFT_HZ 4
29#elif HZ >= 24 && HZ < 48
30# define SHIFT_HZ 5
31#elif HZ >= 48 && HZ < 96
32# define SHIFT_HZ 6
33#elif HZ >= 96 && HZ < 192
34# define SHIFT_HZ 7
35#elif HZ >= 192 && HZ < 384
36# define SHIFT_HZ 8
37#elif HZ >= 384 && HZ < 768
38# define SHIFT_HZ 9
39#elif HZ >= 768 && HZ < 1536
40# define SHIFT_HZ 10
41#else
42# error You lose.
43#endif
44
45/* LATCH is used in the interval timer and ftape setup. */
46#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */
47
48/* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, the we can
49 * improve accuracy by shifting LSH bits, hence calculating:
50 * (NOM << LSH) / DEN
51 * This however means trouble for large NOM, because (NOM << LSH) may no
52 * longer fit in 32 bits. The following way of calculating this gives us
53 * some slack, under the following conditions:
54 * - (NOM / DEN) fits in (32 - LSH) bits.
55 * - (NOM % DEN) fits in (32 - LSH) bits.
56 */
57#define SH_DIV(NOM,DEN,LSH) ( ((NOM / DEN) << LSH) \
58 + (((NOM % DEN) << LSH) + DEN / 2) / DEN)
59
60/* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
61#define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
62
63/* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */
64#define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8))
65
66/* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
67#define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
68
69/* TICK_USEC_TO_NSEC is the time between ticks in nsec assuming real ACTHZ and */
70/* a value TUSEC for TICK_USEC (can be set bij adjtimex) */
71#define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8))
72
73/* some arch's have a small-data section that can be accessed register-relative
74 * but that can only take up to, say, 4-byte variables. jiffies being part of
75 * an 8-byte variable may not be correctly accessed unless we force the issue
76 */
77#define __jiffy_data __attribute__((section(".data")))
78
79/*
80 * The 64-bit value is not volatile - you MUST NOT read it
81 * without sampling the sequence number in xtime_lock.
82 * get_jiffies_64() will do this for you as appropriate.
83 */
84extern u64 __jiffy_data jiffies_64;
85extern unsigned long volatile __jiffy_data jiffies;
86
87#if (BITS_PER_LONG < 64)
88u64 get_jiffies_64(void);
89#else
90static inline u64 get_jiffies_64(void)
91{
92 return (u64)jiffies;
93}
94#endif
95
96/*
97 * These inlines deal with timer wrapping correctly. You are
98 * strongly encouraged to use them
99 * 1. Because people otherwise forget
100 * 2. Because if the timer wrap changes in future you won't have to
101 * alter your driver code.
102 *
103 * time_after(a,b) returns true if the time a is after time b.
104 *
105 * Do this with "<0" and ">=0" to only test the sign of the result. A
106 * good compiler would generate better code (and a really good compiler
107 * wouldn't care). Gcc is currently neither.
108 */
109#define time_after(a,b) \
110 (typecheck(unsigned long, a) && \
111 typecheck(unsigned long, b) && \
112 ((long)(b) - (long)(a) < 0))
113#define time_before(a,b) time_after(b,a)
114
115#define time_after_eq(a,b) \
116 (typecheck(unsigned long, a) && \
117 typecheck(unsigned long, b) && \
118 ((long)(a) - (long)(b) >= 0))
119#define time_before_eq(a,b) time_after_eq(b,a)
120
121/*
122 * Have the 32 bit jiffies value wrap 5 minutes after boot
123 * so jiffies wrap bugs show up earlier.
124 */
125#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
126
127/*
128 * Change timeval to jiffies, trying to avoid the
129 * most obvious overflows..
130 *
131 * And some not so obvious.
132 *
133 * Note that we don't want to return MAX_LONG, because
134 * for various timeout reasons we often end up having
135 * to wait "jiffies+1" in order to guarantee that we wait
136 * at _least_ "jiffies" - so "jiffies+1" had better still
137 * be positive.
138 */
139#define MAX_JIFFY_OFFSET ((~0UL >> 1)-1)
140
141/*
142 * We want to do realistic conversions of time so we need to use the same
143 * values the update wall clock code uses as the jiffies size. This value
144 * is: TICK_NSEC (which is defined in timex.h). This
145 * is a constant and is in nanoseconds. We will used scaled math
146 * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and
147 * NSEC_JIFFIE_SC. Note that these defines contain nothing but
148 * constants and so are computed at compile time. SHIFT_HZ (computed in
149 * timex.h) adjusts the scaling for different HZ values.
150
151 * Scaled math??? What is that?
152 *
153 * Scaled math is a way to do integer math on values that would,
154 * otherwise, either overflow, underflow, or cause undesired div
155 * instructions to appear in the execution path. In short, we "scale"
156 * up the operands so they take more bits (more precision, less
157 * underflow), do the desired operation and then "scale" the result back
158 * by the same amount. If we do the scaling by shifting we avoid the
159 * costly mpy and the dastardly div instructions.
160
161 * Suppose, for example, we want to convert from seconds to jiffies
162 * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The
163 * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
164 * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
165 * might calculate at compile time, however, the result will only have
166 * about 3-4 bits of precision (less for smaller values of HZ).
167 *
168 * So, we scale as follows:
169 * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
170 * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
171 * Then we make SCALE a power of two so:
172 * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
173 * Now we define:
174 * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
175 * jiff = (sec * SEC_CONV) >> SCALE;
176 *
177 * Often the math we use will expand beyond 32-bits so we tell C how to
178 * do this and pass the 64-bit result of the mpy through the ">> SCALE"
179 * which should take the result back to 32-bits. We want this expansion
180 * to capture as much precision as possible. At the same time we don't
181 * want to overflow so we pick the SCALE to avoid this. In this file,
182 * that means using a different scale for each range of HZ values (as
183 * defined in timex.h).
184 *
185 * For those who want to know, gcc will give a 64-bit result from a "*"
186 * operator if the result is a long long AND at least one of the
187 * operands is cast to long long (usually just prior to the "*" so as
188 * not to confuse it into thinking it really has a 64-bit operand,
189 * which, buy the way, it can do, but it take more code and at least 2
190 * mpys).
191
192 * We also need to be aware that one second in nanoseconds is only a
193 * couple of bits away from overflowing a 32-bit word, so we MUST use
194 * 64-bits to get the full range time in nanoseconds.
195
196 */
197
198/*
199 * Here are the scales we will use. One for seconds, nanoseconds and
200 * microseconds.
201 *
202 * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
203 * check if the sign bit is set. If not, we bump the shift count by 1.
204 * (Gets an extra bit of precision where we can use it.)
205 * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
206 * Haven't tested others.
207
208 * Limits of cpp (for #if expressions) only long (no long long), but
209 * then we only need the most signicant bit.
210 */
211
212#define SEC_JIFFIE_SC (31 - SHIFT_HZ)
213#if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
214#undef SEC_JIFFIE_SC
215#define SEC_JIFFIE_SC (32 - SHIFT_HZ)
216#endif
217#define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
218#define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
219#define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
220 TICK_NSEC -1) / (u64)TICK_NSEC))
221
222#define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
223 TICK_NSEC -1) / (u64)TICK_NSEC))
224#define USEC_CONVERSION \
225 ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
226 TICK_NSEC -1) / (u64)TICK_NSEC))
227/*
228 * USEC_ROUND is used in the timeval to jiffie conversion. See there
229 * for more details. It is the scaled resolution rounding value. Note
230 * that it is a 64-bit value. Since, when it is applied, we are already
231 * in jiffies (albit scaled), it is nothing but the bits we will shift
232 * off.
233 */
234#define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
235/*
236 * The maximum jiffie value is (MAX_INT >> 1). Here we translate that
237 * into seconds. The 64-bit case will overflow if we are not careful,
238 * so use the messy SH_DIV macro to do it. Still all constants.
239 */
240#if BITS_PER_LONG < 64
241# define MAX_SEC_IN_JIFFIES \
242 (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
243#else /* take care of overflow on 64 bits machines */
244# define MAX_SEC_IN_JIFFIES \
245 (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
246
247#endif
248
249/*
250 * Convert jiffies to milliseconds and back.
251 *
252 * Avoid unnecessary multiplications/divisions in the
253 * two most common HZ cases:
254 */
255static inline unsigned int jiffies_to_msecs(const unsigned long j)
256{
257#if HZ <= 1000 && !(1000 % HZ)
258 return (1000 / HZ) * j;
259#elif HZ > 1000 && !(HZ % 1000)
260 return (j + (HZ / 1000) - 1)/(HZ / 1000);
261#else
262 return (j * 1000) / HZ;
263#endif
264}
265
266static inline unsigned int jiffies_to_usecs(const unsigned long j)
267{
268#if HZ <= 1000000 && !(1000000 % HZ)
269 return (1000000 / HZ) * j;
270#elif HZ > 1000000 && !(HZ % 1000000)
271 return (j + (HZ / 1000000) - 1)/(HZ / 1000000);
272#else
273 return (j * 1000000) / HZ;
274#endif
275}
276
277static inline unsigned long msecs_to_jiffies(const unsigned int m)
278{
279 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
280 return MAX_JIFFY_OFFSET;
281#if HZ <= 1000 && !(1000 % HZ)
282 return (m + (1000 / HZ) - 1) / (1000 / HZ);
283#elif HZ > 1000 && !(HZ % 1000)
284 return m * (HZ / 1000);
285#else
286 return (m * HZ + 999) / 1000;
287#endif
288}
289
290static inline unsigned long usecs_to_jiffies(const unsigned int u)
291{
292 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
293 return MAX_JIFFY_OFFSET;
294#if HZ <= 1000000 && !(1000000 % HZ)
295 return (u + (1000000 / HZ) - 1) / (1000000 / HZ);
296#elif HZ > 1000000 && !(HZ % 1000000)
297 return u * (HZ / 1000000);
298#else
299 return (u * HZ + 999999) / 1000000;
300#endif
301}
302
303/*
304 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
305 * that a remainder subtract here would not do the right thing as the
306 * resolution values don't fall on second boundries. I.e. the line:
307 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
308 *
309 * Rather, we just shift the bits off the right.
310 *
311 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
312 * value to a scaled second value.
313 */
314static __inline__ unsigned long
315timespec_to_jiffies(const struct timespec *value)
316{
317 unsigned long sec = value->tv_sec;
318 long nsec = value->tv_nsec + TICK_NSEC - 1;
319
320 if (sec >= MAX_SEC_IN_JIFFIES){
321 sec = MAX_SEC_IN_JIFFIES;
322 nsec = 0;
323 }
324 return (((u64)sec * SEC_CONVERSION) +
325 (((u64)nsec * NSEC_CONVERSION) >>
326 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
327
328}
329
330static __inline__ void
331jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
332{
333 /*
334 * Convert jiffies to nanoseconds and separate with
335 * one divide.
336 */
337 u64 nsec = (u64)jiffies * TICK_NSEC;
338 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec);
339}
340
341/* Same for "timeval"
342 *
343 * Well, almost. The problem here is that the real system resolution is
344 * in nanoseconds and the value being converted is in micro seconds.
345 * Also for some machines (those that use HZ = 1024, in-particular),
346 * there is a LARGE error in the tick size in microseconds.
347
348 * The solution we use is to do the rounding AFTER we convert the
349 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
350 * Instruction wise, this should cost only an additional add with carry
351 * instruction above the way it was done above.
352 */
353static __inline__ unsigned long
354timeval_to_jiffies(const struct timeval *value)
355{
356 unsigned long sec = value->tv_sec;
357 long usec = value->tv_usec;
358
359 if (sec >= MAX_SEC_IN_JIFFIES){
360 sec = MAX_SEC_IN_JIFFIES;
361 usec = 0;
362 }
363 return (((u64)sec * SEC_CONVERSION) +
364 (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
365 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
366}
367
368static __inline__ void
369jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
370{
371 /*
372 * Convert jiffies to nanoseconds and separate with
373 * one divide.
374 */
375 u64 nsec = (u64)jiffies * TICK_NSEC;
376 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_usec);
377 value->tv_usec /= NSEC_PER_USEC;
378}
379
380/*
381 * Convert jiffies/jiffies_64 to clock_t and back.
382 */
383static inline clock_t jiffies_to_clock_t(long x)
384{
385#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
386 return x / (HZ / USER_HZ);
387#else
388 u64 tmp = (u64)x * TICK_NSEC;
389 do_div(tmp, (NSEC_PER_SEC / USER_HZ));
390 return (long)tmp;
391#endif
392}
393
394static inline unsigned long clock_t_to_jiffies(unsigned long x)
395{
396#if (HZ % USER_HZ)==0
397 if (x >= ~0UL / (HZ / USER_HZ))
398 return ~0UL;
399 return x * (HZ / USER_HZ);
400#else
401 u64 jif;
402
403 /* Don't worry about loss of precision here .. */
404 if (x >= ~0UL / HZ * USER_HZ)
405 return ~0UL;
406
407 /* .. but do try to contain it here */
408 jif = x * (u64) HZ;
409 do_div(jif, USER_HZ);
410 return jif;
411#endif
412}
413
414static inline u64 jiffies_64_to_clock_t(u64 x)
415{
416#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
417 do_div(x, HZ / USER_HZ);
418#else
419 /*
420 * There are better ways that don't overflow early,
421 * but even this doesn't overflow in hundreds of years
422 * in 64 bits, so..
423 */
424 x *= TICK_NSEC;
425 do_div(x, (NSEC_PER_SEC / USER_HZ));
426#endif
427 return x;
428}
429
430static inline u64 nsec_to_clock_t(u64 x)
431{
432#if (NSEC_PER_SEC % USER_HZ) == 0
433 do_div(x, (NSEC_PER_SEC / USER_HZ));
434#elif (USER_HZ % 512) == 0
435 x *= USER_HZ/512;
436 do_div(x, (NSEC_PER_SEC / 512));
437#else
438 /*
439 * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
440 * overflow after 64.99 years.
441 * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
442 */
443 x *= 9;
444 do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2))
445 / USER_HZ));
446#endif
447 return x;
448}
449
450#endif