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 #define LATCH_HPET ((HPET_TICK_RATE + HZ/2) / HZ)
40
41 /* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, the we can
42 * improve accuracy by shifting LSH bits, hence calculating:
43 * (NOM << LSH) / DEN
44 * This however means trouble for large NOM, because (NOM << LSH) may no
45 * longer fit in 32 bits. The following way of calculating this gives us
46 * some slack, under the following conditions:
47 * - (NOM / DEN) fits in (32 - LSH) bits.
48 * - (NOM % DEN) fits in (32 - LSH) bits.
49 */
50 #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \
51 + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
52
53 /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
54 #define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
55
56 #define ACTHZ_HPET (SH_DIV (HPET_TICK_RATE, LATCH_HPET, 8))
57
58 /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */
59 #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8))
60
61 #define TICK_NSEC_HPET (SH_DIV(1000000UL * 1000, ACTHZ_HPET, 8))
62
63 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
64 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
65
66 /* TICK_USEC_TO_NSEC is the time between ticks in nsec assuming real ACTHZ and */
67 /* a value TUSEC for TICK_USEC (can be set bij adjtimex) */
68 #define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8))
69
70 /* some arch's have a small-data section that can be accessed register-relative
71 * but that can only take up to, say, 4-byte variables. jiffies being part of
72 * an 8-byte variable may not be correctly accessed unless we force the issue
73 */
74 #define __jiffy_data __attribute__((section(".data")))
75
76 /*
77 * The 64-bit value is not volatile - you MUST NOT read it
78 * without sampling the sequence number in xtime_lock.
79 * get_jiffies_64() will do this for you as appropriate.
80 */
81 extern u64 __jiffy_data jiffies_64;
82 extern unsigned long volatile __jiffy_data jiffies;
83
84 #if (BITS_PER_LONG < 64)
85 u64 get_jiffies_64(void);
86 #else
get_jiffies_64(void)87 static inline u64 get_jiffies_64(void)
88 {
89 return (u64)jiffies;
90 }
91 #endif
92
93 /*
94 * These inlines deal with timer wrapping correctly. You are
95 * strongly encouraged to use them
96 * 1. Because people otherwise forget
97 * 2. Because if the timer wrap changes in future you won't have to
98 * alter your driver code.
99 *
100 * time_after(a,b) returns true if the time a is after time b.
101 *
102 * Do this with "<0" and ">=0" to only test the sign of the result. A
103 * good compiler would generate better code (and a really good compiler
104 * wouldn't care). Gcc is currently neither.
105 */
106 #define time_after(a,b) \
107 (typecheck(unsigned long, a) && \
108 typecheck(unsigned long, b) && \
109 ((long)(b) - (long)(a) < 0))
110 #define time_before(a,b) time_after(b,a)
111
112 #define time_after_eq(a,b) \
113 (typecheck(unsigned long, a) && \
114 typecheck(unsigned long, b) && \
115 ((long)(a) - (long)(b) >= 0))
116 #define time_before_eq(a,b) time_after_eq(b,a)
117
118 /*
119 * Have the 32 bit jiffies value wrap 5 minutes after boot
120 * so jiffies wrap bugs show up earlier.
121 */
122 #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
123
124 /*
125 * Change timeval to jiffies, trying to avoid the
126 * most obvious overflows..
127 *
128 * And some not so obvious.
129 *
130 * Note that we don't want to return MAX_LONG, because
131 * for various timeout reasons we often end up having
132 * to wait "jiffies+1" in order to guarantee that we wait
133 * at _least_ "jiffies" - so "jiffies+1" had better still
134 * be positive.
135 */
136 #define MAX_JIFFY_OFFSET ((~0UL >> 1)-1)
137
138 /*
139 * We want to do realistic conversions of time so we need to use the same
140 * values the update wall clock code uses as the jiffies size. This value
141 * is: TICK_NSEC (which is defined in timex.h). This
142 * is a constant and is in nanoseconds. We will used scaled math
143 * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and
144 * NSEC_JIFFIE_SC. Note that these defines contain nothing but
145 * constants and so are computed at compile time. SHIFT_HZ (computed in
146 * timex.h) adjusts the scaling for different HZ values.
147
148 * Scaled math??? What is that?
149 *
150 * Scaled math is a way to do integer math on values that would,
151 * otherwise, either overflow, underflow, or cause undesired div
152 * instructions to appear in the execution path. In short, we "scale"
153 * up the operands so they take more bits (more precision, less
154 * underflow), do the desired operation and then "scale" the result back
155 * by the same amount. If we do the scaling by shifting we avoid the
156 * costly mpy and the dastardly div instructions.
157
158 * Suppose, for example, we want to convert from seconds to jiffies
159 * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The
160 * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
161 * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
162 * might calculate at compile time, however, the result will only have
163 * about 3-4 bits of precision (less for smaller values of HZ).
164 *
165 * So, we scale as follows:
166 * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
167 * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
168 * Then we make SCALE a power of two so:
169 * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
170 * Now we define:
171 * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
172 * jiff = (sec * SEC_CONV) >> SCALE;
173 *
174 * Often the math we use will expand beyond 32-bits so we tell C how to
175 * do this and pass the 64-bit result of the mpy through the ">> SCALE"
176 * which should take the result back to 32-bits. We want this expansion
177 * to capture as much precision as possible. At the same time we don't
178 * want to overflow so we pick the SCALE to avoid this. In this file,
179 * that means using a different scale for each range of HZ values (as
180 * defined in timex.h).
181 *
182 * For those who want to know, gcc will give a 64-bit result from a "*"
183 * operator if the result is a long long AND at least one of the
184 * operands is cast to long long (usually just prior to the "*" so as
185 * not to confuse it into thinking it really has a 64-bit operand,
186 * which, buy the way, it can do, but it take more code and at least 2
187 * mpys).
188
189 * We also need to be aware that one second in nanoseconds is only a
190 * couple of bits away from overflowing a 32-bit word, so we MUST use
191 * 64-bits to get the full range time in nanoseconds.
192
193 */
194
195 /*
196 * Here are the scales we will use. One for seconds, nanoseconds and
197 * microseconds.
198 *
199 * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
200 * check if the sign bit is set. If not, we bump the shift count by 1.
201 * (Gets an extra bit of precision where we can use it.)
202 * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
203 * Haven't tested others.
204
205 * Limits of cpp (for #if expressions) only long (no long long), but
206 * then we only need the most signicant bit.
207 */
208
209 #define SEC_JIFFIE_SC (31 - SHIFT_HZ)
210 #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
211 #undef SEC_JIFFIE_SC
212 #define SEC_JIFFIE_SC (32 - SHIFT_HZ)
213 #endif
214 #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
215 #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
216 #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
217 TICK_NSEC -1) / (u64)TICK_NSEC))
218
219 #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
220 TICK_NSEC -1) / (u64)TICK_NSEC))
221 #define USEC_CONVERSION \
222 ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
223 TICK_NSEC -1) / (u64)TICK_NSEC))
224 /*
225 * USEC_ROUND is used in the timeval to jiffie conversion. See there
226 * for more details. It is the scaled resolution rounding value. Note
227 * that it is a 64-bit value. Since, when it is applied, we are already
228 * in jiffies (albit scaled), it is nothing but the bits we will shift
229 * off.
230 */
231 #define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
232 /*
233 * The maximum jiffie value is (MAX_INT >> 1). Here we translate that
234 * into seconds. The 64-bit case will overflow if we are not careful,
235 * so use the messy SH_DIV macro to do it. Still all constants.
236 */
237 #if BITS_PER_LONG < 64
238 # define MAX_SEC_IN_JIFFIES \
239 (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
240 #else /* take care of overflow on 64 bits machines */
241 # define MAX_SEC_IN_JIFFIES \
242 (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
243
244 #endif
245
246 /*
247 * Convert jiffies to milliseconds and back.
248 *
249 * Avoid unnecessary multiplications/divisions in the
250 * two most common HZ cases:
251 */
jiffies_to_msecs(const unsigned long j)252 static inline unsigned int jiffies_to_msecs(const unsigned long j)
253 {
254 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
255 return (MSEC_PER_SEC / HZ) * j;
256 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
257 return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
258 #else
259 return (j * MSEC_PER_SEC) / HZ;
260 #endif
261 }
262
jiffies_to_usecs(const unsigned long j)263 static inline unsigned int jiffies_to_usecs(const unsigned long j)
264 {
265 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
266 return (USEC_PER_SEC / HZ) * j;
267 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
268 return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
269 #else
270 return (j * USEC_PER_SEC) / HZ;
271 #endif
272 }
273
msecs_to_jiffies(const unsigned int m)274 static inline unsigned long msecs_to_jiffies(const unsigned int m)
275 {
276 if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
277 return MAX_JIFFY_OFFSET;
278 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
279 return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
280 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
281 return m * (HZ / MSEC_PER_SEC);
282 #else
283 return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC;
284 #endif
285 }
286
usecs_to_jiffies(const unsigned int u)287 static inline unsigned long usecs_to_jiffies(const unsigned int u)
288 {
289 if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
290 return MAX_JIFFY_OFFSET;
291 #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
292 return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
293 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
294 return u * (HZ / USEC_PER_SEC);
295 #else
296 return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC;
297 #endif
298 }
299
300 /*
301 * The TICK_NSEC - 1 rounds up the value to the next resolution. Note
302 * that a remainder subtract here would not do the right thing as the
303 * resolution values don't fall on second boundries. I.e. the line:
304 * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding.
305 *
306 * Rather, we just shift the bits off the right.
307 *
308 * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec
309 * value to a scaled second value.
310 */
311 static __inline__ unsigned long
timespec_to_jiffies(const struct timespec * value)312 timespec_to_jiffies(const struct timespec *value)
313 {
314 unsigned long sec = value->tv_sec;
315 long nsec = value->tv_nsec + TICK_NSEC - 1;
316
317 if (sec >= MAX_SEC_IN_JIFFIES){
318 sec = MAX_SEC_IN_JIFFIES;
319 nsec = 0;
320 }
321 return (((u64)sec * SEC_CONVERSION) +
322 (((u64)nsec * NSEC_CONVERSION) >>
323 (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
324
325 }
326
327 static __inline__ void
jiffies_to_timespec(const unsigned long jiffies,struct timespec * value)328 jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
329 {
330 /*
331 * Convert jiffies to nanoseconds and separate with
332 * one divide.
333 */
334 u64 nsec = (u64)jiffies * TICK_NSEC;
335 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec);
336 }
337
338 /* Same for "timeval"
339 *
340 * Well, almost. The problem here is that the real system resolution is
341 * in nanoseconds and the value being converted is in micro seconds.
342 * Also for some machines (those that use HZ = 1024, in-particular),
343 * there is a LARGE error in the tick size in microseconds.
344
345 * The solution we use is to do the rounding AFTER we convert the
346 * microsecond part. Thus the USEC_ROUND, the bits to be shifted off.
347 * Instruction wise, this should cost only an additional add with carry
348 * instruction above the way it was done above.
349 */
350 static __inline__ unsigned long
timeval_to_jiffies(const struct timeval * value)351 timeval_to_jiffies(const struct timeval *value)
352 {
353 unsigned long sec = value->tv_sec;
354 long usec = value->tv_usec;
355
356 if (sec >= MAX_SEC_IN_JIFFIES){
357 sec = MAX_SEC_IN_JIFFIES;
358 usec = 0;
359 }
360 return (((u64)sec * SEC_CONVERSION) +
361 (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
362 (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC;
363 }
364
365 static __inline__ void
jiffies_to_timeval(const unsigned long jiffies,struct timeval * value)366 jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
367 {
368 /*
369 * Convert jiffies to nanoseconds and separate with
370 * one divide.
371 */
372 u64 nsec = (u64)jiffies * TICK_NSEC;
373 long tv_usec;
374
375 value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tv_usec);
376 tv_usec /= NSEC_PER_USEC;
377 value->tv_usec = tv_usec;
378 }
379
380 /*
381 * Convert jiffies/jiffies_64 to clock_t and back.
382 */
jiffies_to_clock_t(long x)383 static 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
clock_t_to_jiffies(unsigned long x)394 static 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
jiffies_64_to_clock_t(u64 x)414 static 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
nsec_to_clock_t(u64 x)430 static 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
451