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1da177e4 LT |
1 | #ifndef _LINUX_JIFFIES_H |
2 | #define _LINUX_JIFFIES_H | |
3 | ||
5cca7619 | 4 | #include <linux/calc64.h> |
1da177e4 LT |
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 */ | |
1da177e4 LT |
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 | ||
b20367a6 JH |
39 | #define LATCH_HPET ((HPET_TICK_RATE + HZ/2) / HZ) |
40 | ||
1da177e4 LT |
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 | */ | |
0d94df56 UZ |
50 | #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \ |
51 | + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN)) | |
1da177e4 LT |
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 | ||
b20367a6 JH |
56 | #define ACTHZ_HPET (SH_DIV (HPET_TICK_RATE, LATCH_HPET, 8)) |
57 | ||
1da177e4 LT |
58 | /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */ |
59 | #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8)) | |
60 | ||
b20367a6 JH |
61 | #define TICK_NSEC_HPET (SH_DIV(1000000UL * 1000, ACTHZ_HPET, 8)) |
62 | ||
1da177e4 LT |
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 | |
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 | ||
3b171672 DZ |
118 | /* Same as above, but does so with platform independent 64bit types. |
119 | * These must be used when utilizing jiffies_64 (i.e. return value of | |
120 | * get_jiffies_64() */ | |
121 | #define time_after64(a,b) \ | |
122 | (typecheck(__u64, a) && \ | |
123 | typecheck(__u64, b) && \ | |
124 | ((__s64)(b) - (__s64)(a) < 0)) | |
125 | #define time_before64(a,b) time_after64(b,a) | |
126 | ||
127 | #define time_after_eq64(a,b) \ | |
128 | (typecheck(__u64, a) && \ | |
129 | typecheck(__u64, b) && \ | |
130 | ((__s64)(a) - (__s64)(b) >= 0)) | |
131 | #define time_before_eq64(a,b) time_after_eq64(b,a) | |
132 | ||
1da177e4 LT |
133 | /* |
134 | * Have the 32 bit jiffies value wrap 5 minutes after boot | |
135 | * so jiffies wrap bugs show up earlier. | |
136 | */ | |
137 | #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ)) | |
138 | ||
139 | /* | |
140 | * Change timeval to jiffies, trying to avoid the | |
141 | * most obvious overflows.. | |
142 | * | |
143 | * And some not so obvious. | |
144 | * | |
145 | * Note that we don't want to return MAX_LONG, because | |
146 | * for various timeout reasons we often end up having | |
147 | * to wait "jiffies+1" in order to guarantee that we wait | |
148 | * at _least_ "jiffies" - so "jiffies+1" had better still | |
149 | * be positive. | |
150 | */ | |
151 | #define MAX_JIFFY_OFFSET ((~0UL >> 1)-1) | |
152 | ||
153 | /* | |
154 | * We want to do realistic conversions of time so we need to use the same | |
155 | * values the update wall clock code uses as the jiffies size. This value | |
156 | * is: TICK_NSEC (which is defined in timex.h). This | |
157 | * is a constant and is in nanoseconds. We will used scaled math | |
158 | * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and | |
159 | * NSEC_JIFFIE_SC. Note that these defines contain nothing but | |
160 | * constants and so are computed at compile time. SHIFT_HZ (computed in | |
161 | * timex.h) adjusts the scaling for different HZ values. | |
162 | ||
163 | * Scaled math??? What is that? | |
164 | * | |
165 | * Scaled math is a way to do integer math on values that would, | |
166 | * otherwise, either overflow, underflow, or cause undesired div | |
167 | * instructions to appear in the execution path. In short, we "scale" | |
168 | * up the operands so they take more bits (more precision, less | |
169 | * underflow), do the desired operation and then "scale" the result back | |
170 | * by the same amount. If we do the scaling by shifting we avoid the | |
171 | * costly mpy and the dastardly div instructions. | |
172 | ||
173 | * Suppose, for example, we want to convert from seconds to jiffies | |
174 | * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The | |
175 | * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We | |
176 | * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we | |
177 | * might calculate at compile time, however, the result will only have | |
178 | * about 3-4 bits of precision (less for smaller values of HZ). | |
179 | * | |
180 | * So, we scale as follows: | |
181 | * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE); | |
182 | * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE; | |
183 | * Then we make SCALE a power of two so: | |
184 | * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE; | |
185 | * Now we define: | |
186 | * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) | |
187 | * jiff = (sec * SEC_CONV) >> SCALE; | |
188 | * | |
189 | * Often the math we use will expand beyond 32-bits so we tell C how to | |
190 | * do this and pass the 64-bit result of the mpy through the ">> SCALE" | |
191 | * which should take the result back to 32-bits. We want this expansion | |
192 | * to capture as much precision as possible. At the same time we don't | |
193 | * want to overflow so we pick the SCALE to avoid this. In this file, | |
194 | * that means using a different scale for each range of HZ values (as | |
195 | * defined in timex.h). | |
196 | * | |
197 | * For those who want to know, gcc will give a 64-bit result from a "*" | |
198 | * operator if the result is a long long AND at least one of the | |
199 | * operands is cast to long long (usually just prior to the "*" so as | |
200 | * not to confuse it into thinking it really has a 64-bit operand, | |
201 | * which, buy the way, it can do, but it take more code and at least 2 | |
202 | * mpys). | |
203 | ||
204 | * We also need to be aware that one second in nanoseconds is only a | |
205 | * couple of bits away from overflowing a 32-bit word, so we MUST use | |
206 | * 64-bits to get the full range time in nanoseconds. | |
207 | ||
208 | */ | |
209 | ||
210 | /* | |
211 | * Here are the scales we will use. One for seconds, nanoseconds and | |
212 | * microseconds. | |
213 | * | |
214 | * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and | |
215 | * check if the sign bit is set. If not, we bump the shift count by 1. | |
216 | * (Gets an extra bit of precision where we can use it.) | |
217 | * We know it is set for HZ = 1024 and HZ = 100 not for 1000. | |
218 | * Haven't tested others. | |
219 | ||
220 | * Limits of cpp (for #if expressions) only long (no long long), but | |
221 | * then we only need the most signicant bit. | |
222 | */ | |
223 | ||
224 | #define SEC_JIFFIE_SC (31 - SHIFT_HZ) | |
225 | #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000) | |
226 | #undef SEC_JIFFIE_SC | |
227 | #define SEC_JIFFIE_SC (32 - SHIFT_HZ) | |
228 | #endif | |
229 | #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29) | |
230 | #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19) | |
231 | #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\ | |
232 | TICK_NSEC -1) / (u64)TICK_NSEC)) | |
233 | ||
234 | #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\ | |
235 | TICK_NSEC -1) / (u64)TICK_NSEC)) | |
236 | #define USEC_CONVERSION \ | |
237 | ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\ | |
238 | TICK_NSEC -1) / (u64)TICK_NSEC)) | |
239 | /* | |
240 | * USEC_ROUND is used in the timeval to jiffie conversion. See there | |
241 | * for more details. It is the scaled resolution rounding value. Note | |
242 | * that it is a 64-bit value. Since, when it is applied, we are already | |
243 | * in jiffies (albit scaled), it is nothing but the bits we will shift | |
244 | * off. | |
245 | */ | |
246 | #define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1) | |
247 | /* | |
248 | * The maximum jiffie value is (MAX_INT >> 1). Here we translate that | |
249 | * into seconds. The 64-bit case will overflow if we are not careful, | |
250 | * so use the messy SH_DIV macro to do it. Still all constants. | |
251 | */ | |
252 | #if BITS_PER_LONG < 64 | |
253 | # define MAX_SEC_IN_JIFFIES \ | |
254 | (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC) | |
255 | #else /* take care of overflow on 64 bits machines */ | |
256 | # define MAX_SEC_IN_JIFFIES \ | |
257 | (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1) | |
258 | ||
259 | #endif | |
260 | ||
261 | /* | |
262 | * Convert jiffies to milliseconds and back. | |
263 | * | |
264 | * Avoid unnecessary multiplications/divisions in the | |
265 | * two most common HZ cases: | |
266 | */ | |
267 | static inline unsigned int jiffies_to_msecs(const unsigned long j) | |
268 | { | |
84f902c0 NA |
269 | #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) |
270 | return (MSEC_PER_SEC / HZ) * j; | |
271 | #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) | |
272 | return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); | |
1da177e4 | 273 | #else |
84f902c0 | 274 | return (j * MSEC_PER_SEC) / HZ; |
1da177e4 LT |
275 | #endif |
276 | } | |
277 | ||
278 | static inline unsigned int jiffies_to_usecs(const unsigned long j) | |
279 | { | |
84f902c0 NA |
280 | #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) |
281 | return (USEC_PER_SEC / HZ) * j; | |
282 | #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) | |
283 | return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC); | |
1da177e4 | 284 | #else |
84f902c0 | 285 | return (j * USEC_PER_SEC) / HZ; |
1da177e4 LT |
286 | #endif |
287 | } | |
288 | ||
289 | static inline unsigned long msecs_to_jiffies(const unsigned int m) | |
290 | { | |
291 | if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET)) | |
292 | return MAX_JIFFY_OFFSET; | |
84f902c0 NA |
293 | #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) |
294 | return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ); | |
295 | #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) | |
296 | return m * (HZ / MSEC_PER_SEC); | |
1da177e4 | 297 | #else |
84f902c0 | 298 | return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC; |
1da177e4 LT |
299 | #endif |
300 | } | |
301 | ||
302 | static inline unsigned long usecs_to_jiffies(const unsigned int u) | |
303 | { | |
304 | if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET)) | |
305 | return MAX_JIFFY_OFFSET; | |
84f902c0 NA |
306 | #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) |
307 | return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ); | |
308 | #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) | |
309 | return u * (HZ / USEC_PER_SEC); | |
1da177e4 | 310 | #else |
84f902c0 | 311 | return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC; |
1da177e4 LT |
312 | #endif |
313 | } | |
314 | ||
315 | /* | |
316 | * The TICK_NSEC - 1 rounds up the value to the next resolution. Note | |
317 | * that a remainder subtract here would not do the right thing as the | |
318 | * resolution values don't fall on second boundries. I.e. the line: | |
319 | * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding. | |
320 | * | |
321 | * Rather, we just shift the bits off the right. | |
322 | * | |
323 | * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec | |
324 | * value to a scaled second value. | |
325 | */ | |
326 | static __inline__ unsigned long | |
327 | timespec_to_jiffies(const struct timespec *value) | |
328 | { | |
329 | unsigned long sec = value->tv_sec; | |
330 | long nsec = value->tv_nsec + TICK_NSEC - 1; | |
331 | ||
332 | if (sec >= MAX_SEC_IN_JIFFIES){ | |
333 | sec = MAX_SEC_IN_JIFFIES; | |
334 | nsec = 0; | |
335 | } | |
336 | return (((u64)sec * SEC_CONVERSION) + | |
337 | (((u64)nsec * NSEC_CONVERSION) >> | |
338 | (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; | |
339 | ||
340 | } | |
341 | ||
342 | static __inline__ void | |
343 | jiffies_to_timespec(const unsigned long jiffies, struct timespec *value) | |
344 | { | |
345 | /* | |
346 | * Convert jiffies to nanoseconds and separate with | |
347 | * one divide. | |
348 | */ | |
349 | u64 nsec = (u64)jiffies * TICK_NSEC; | |
350 | value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec); | |
351 | } | |
352 | ||
353 | /* Same for "timeval" | |
354 | * | |
355 | * Well, almost. The problem here is that the real system resolution is | |
356 | * in nanoseconds and the value being converted is in micro seconds. | |
357 | * Also for some machines (those that use HZ = 1024, in-particular), | |
358 | * there is a LARGE error in the tick size in microseconds. | |
359 | ||
360 | * The solution we use is to do the rounding AFTER we convert the | |
361 | * microsecond part. Thus the USEC_ROUND, the bits to be shifted off. | |
362 | * Instruction wise, this should cost only an additional add with carry | |
363 | * instruction above the way it was done above. | |
364 | */ | |
365 | static __inline__ unsigned long | |
366 | timeval_to_jiffies(const struct timeval *value) | |
367 | { | |
368 | unsigned long sec = value->tv_sec; | |
369 | long usec = value->tv_usec; | |
370 | ||
371 | if (sec >= MAX_SEC_IN_JIFFIES){ | |
372 | sec = MAX_SEC_IN_JIFFIES; | |
373 | usec = 0; | |
374 | } | |
375 | return (((u64)sec * SEC_CONVERSION) + | |
376 | (((u64)usec * USEC_CONVERSION + USEC_ROUND) >> | |
377 | (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; | |
378 | } | |
379 | ||
380 | static __inline__ void | |
381 | jiffies_to_timeval(const unsigned long jiffies, struct timeval *value) | |
382 | { | |
383 | /* | |
384 | * Convert jiffies to nanoseconds and separate with | |
385 | * one divide. | |
386 | */ | |
387 | u64 nsec = (u64)jiffies * TICK_NSEC; | |
5cca7619 TG |
388 | long tv_usec; |
389 | ||
390 | value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tv_usec); | |
391 | tv_usec /= NSEC_PER_USEC; | |
392 | value->tv_usec = tv_usec; | |
1da177e4 LT |
393 | } |
394 | ||
395 | /* | |
396 | * Convert jiffies/jiffies_64 to clock_t and back. | |
397 | */ | |
398 | static inline clock_t jiffies_to_clock_t(long x) | |
399 | { | |
400 | #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 | |
401 | return x / (HZ / USER_HZ); | |
402 | #else | |
403 | u64 tmp = (u64)x * TICK_NSEC; | |
404 | do_div(tmp, (NSEC_PER_SEC / USER_HZ)); | |
405 | return (long)tmp; | |
406 | #endif | |
407 | } | |
408 | ||
409 | static inline unsigned long clock_t_to_jiffies(unsigned long x) | |
410 | { | |
411 | #if (HZ % USER_HZ)==0 | |
412 | if (x >= ~0UL / (HZ / USER_HZ)) | |
413 | return ~0UL; | |
414 | return x * (HZ / USER_HZ); | |
415 | #else | |
416 | u64 jif; | |
417 | ||
418 | /* Don't worry about loss of precision here .. */ | |
419 | if (x >= ~0UL / HZ * USER_HZ) | |
420 | return ~0UL; | |
421 | ||
422 | /* .. but do try to contain it here */ | |
423 | jif = x * (u64) HZ; | |
424 | do_div(jif, USER_HZ); | |
425 | return jif; | |
426 | #endif | |
427 | } | |
428 | ||
429 | static inline u64 jiffies_64_to_clock_t(u64 x) | |
430 | { | |
431 | #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 | |
432 | do_div(x, HZ / USER_HZ); | |
433 | #else | |
434 | /* | |
435 | * There are better ways that don't overflow early, | |
436 | * but even this doesn't overflow in hundreds of years | |
437 | * in 64 bits, so.. | |
438 | */ | |
439 | x *= TICK_NSEC; | |
440 | do_div(x, (NSEC_PER_SEC / USER_HZ)); | |
441 | #endif | |
442 | return x; | |
443 | } | |
444 | ||
445 | static inline u64 nsec_to_clock_t(u64 x) | |
446 | { | |
447 | #if (NSEC_PER_SEC % USER_HZ) == 0 | |
448 | do_div(x, (NSEC_PER_SEC / USER_HZ)); | |
449 | #elif (USER_HZ % 512) == 0 | |
450 | x *= USER_HZ/512; | |
451 | do_div(x, (NSEC_PER_SEC / 512)); | |
452 | #else | |
453 | /* | |
454 | * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024, | |
455 | * overflow after 64.99 years. | |
456 | * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ... | |
457 | */ | |
458 | x *= 9; | |
459 | do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2)) | |
460 | / USER_HZ)); | |
461 | #endif | |
462 | return x; | |
463 | } | |
464 | ||
465 | #endif |