1 #ifndef _LINUX_JIFFIES_H
2 #define _LINUX_JIFFIES_H
4 #include <linux/math64.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 */
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.
18 #if HZ >= 12 && HZ < 24
20 #elif HZ >= 24 && HZ < 48
22 #elif HZ >= 48 && HZ < 96
24 #elif HZ >= 96 && HZ < 192
26 #elif HZ >= 192 && HZ < 384
28 #elif HZ >= 384 && HZ < 768
30 #elif HZ >= 768 && HZ < 1536
32 #elif HZ >= 1536 && HZ < 3072
34 #elif HZ >= 3072 && HZ < 6144
36 #elif HZ >= 6144 && HZ < 12288
39 # error Invalid value of HZ.
42 /* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
43 * improve accuracy by shifting LSH bits, hence calculating:
45 * This however means trouble for large NOM, because (NOM << LSH) may no
46 * longer fit in 32 bits. The following way of calculating this gives us
47 * some slack, under the following conditions:
48 * - (NOM / DEN) fits in (32 - LSH) bits.
49 * - (NOM % DEN) fits in (32 - LSH) bits.
51 #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \
52 + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
54 /* LATCH is used in the interval timer and ftape setup. */
55 #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */
57 #ifdef CLOCK_TICK_RATE
60 * HZ is the requested value. However the CLOCK_TICK_RATE may not allow
61 * for exactly HZ. So SHIFTED_HZ is high res HZ ("<< 8" is for accuracy)
63 # define SHIFTED_HZ (SH_DIV(CLOCK_TICK_RATE, LATCH, 8))
65 # define SHIFTED_HZ (HZ << 8)
68 /* TICK_NSEC is the time between ticks in nsec assuming SHIFTED_HZ */
69 #define TICK_NSEC (SH_DIV(1000000UL * 1000, SHIFTED_HZ, 8))
71 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
72 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
75 * TICK_USEC_TO_NSEC is the time between ticks in nsec assuming SHIFTED_HZ and
76 * a value TUSEC for TICK_USEC (can be set bij adjtimex)
78 #define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV(TUSEC * USER_HZ * 1000, SHIFTED_HZ, 8))
80 /* some arch's have a small-data section that can be accessed register-relative
81 * but that can only take up to, say, 4-byte variables. jiffies being part of
82 * an 8-byte variable may not be correctly accessed unless we force the issue
84 #define __jiffy_data __attribute__((section(".data")))
87 * The 64-bit value is not atomic - you MUST NOT read it
88 * without sampling the sequence number in xtime_lock.
89 * get_jiffies_64() will do this for you as appropriate.
91 extern u64 __jiffy_data jiffies_64;
92 extern unsigned long volatile __jiffy_data jiffies;
94 #if (BITS_PER_LONG < 64)
95 u64 get_jiffies_64(void);
97 static inline u64 get_jiffies_64(void)
104 * These inlines deal with timer wrapping correctly. You are
105 * strongly encouraged to use them
106 * 1. Because people otherwise forget
107 * 2. Because if the timer wrap changes in future you won't have to
108 * alter your driver code.
110 * time_after(a,b) returns true if the time a is after time b.
112 * Do this with "<0" and ">=0" to only test the sign of the result. A
113 * good compiler would generate better code (and a really good compiler
114 * wouldn't care). Gcc is currently neither.
116 #define time_after(a,b) \
117 (typecheck(unsigned long, a) && \
118 typecheck(unsigned long, b) && \
119 ((long)(b) - (long)(a) < 0))
120 #define time_before(a,b) time_after(b,a)
122 #define time_after_eq(a,b) \
123 (typecheck(unsigned long, a) && \
124 typecheck(unsigned long, b) && \
125 ((long)(a) - (long)(b) >= 0))
126 #define time_before_eq(a,b) time_after_eq(b,a)
129 * Calculate whether a is in the range of [b, c].
131 #define time_in_range(a,b,c) \
132 (time_after_eq(a,b) && \
136 * Calculate whether a is in the range of [b, c).
138 #define time_in_range_open(a,b,c) \
139 (time_after_eq(a,b) && \
142 /* Same as above, but does so with platform independent 64bit types.
143 * These must be used when utilizing jiffies_64 (i.e. return value of
144 * get_jiffies_64() */
145 #define time_after64(a,b) \
146 (typecheck(__u64, a) && \
147 typecheck(__u64, b) && \
148 ((__s64)(b) - (__s64)(a) < 0))
149 #define time_before64(a,b) time_after64(b,a)
151 #define time_after_eq64(a,b) \
152 (typecheck(__u64, a) && \
153 typecheck(__u64, b) && \
154 ((__s64)(a) - (__s64)(b) >= 0))
155 #define time_before_eq64(a,b) time_after_eq64(b,a)
158 * These four macros compare jiffies and 'a' for convenience.
161 /* time_is_before_jiffies(a) return true if a is before jiffies */
162 #define time_is_before_jiffies(a) time_after(jiffies, a)
164 /* time_is_after_jiffies(a) return true if a is after jiffies */
165 #define time_is_after_jiffies(a) time_before(jiffies, a)
167 /* time_is_before_eq_jiffies(a) return true if a is before or equal to jiffies*/
168 #define time_is_before_eq_jiffies(a) time_after_eq(jiffies, a)
170 /* time_is_after_eq_jiffies(a) return true if a is after or equal to jiffies*/
171 #define time_is_after_eq_jiffies(a) time_before_eq(jiffies, a)
174 * Have the 32 bit jiffies value wrap 5 minutes after boot
175 * so jiffies wrap bugs show up earlier.
177 #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
180 * Change timeval to jiffies, trying to avoid the
181 * most obvious overflows..
183 * And some not so obvious.
185 * Note that we don't want to return LONG_MAX, because
186 * for various timeout reasons we often end up having
187 * to wait "jiffies+1" in order to guarantee that we wait
188 * at _least_ "jiffies" - so "jiffies+1" had better still
191 #define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1)
193 extern unsigned long preset_lpj;
196 * We want to do realistic conversions of time so we need to use the same
197 * values the update wall clock code uses as the jiffies size. This value
198 * is: TICK_NSEC (which is defined in timex.h). This
199 * is a constant and is in nanoseconds. We will use scaled math
200 * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and
201 * NSEC_JIFFIE_SC. Note that these defines contain nothing but
202 * constants and so are computed at compile time. SHIFT_HZ (computed in
203 * timex.h) adjusts the scaling for different HZ values.
205 * Scaled math??? What is that?
207 * Scaled math is a way to do integer math on values that would,
208 * otherwise, either overflow, underflow, or cause undesired div
209 * instructions to appear in the execution path. In short, we "scale"
210 * up the operands so they take more bits (more precision, less
211 * underflow), do the desired operation and then "scale" the result back
212 * by the same amount. If we do the scaling by shifting we avoid the
213 * costly mpy and the dastardly div instructions.
215 * Suppose, for example, we want to convert from seconds to jiffies
216 * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The
217 * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
218 * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
219 * might calculate at compile time, however, the result will only have
220 * about 3-4 bits of precision (less for smaller values of HZ).
222 * So, we scale as follows:
223 * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
224 * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
225 * Then we make SCALE a power of two so:
226 * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
228 * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
229 * jiff = (sec * SEC_CONV) >> SCALE;
231 * Often the math we use will expand beyond 32-bits so we tell C how to
232 * do this and pass the 64-bit result of the mpy through the ">> SCALE"
233 * which should take the result back to 32-bits. We want this expansion
234 * to capture as much precision as possible. At the same time we don't
235 * want to overflow so we pick the SCALE to avoid this. In this file,
236 * that means using a different scale for each range of HZ values (as
237 * defined in timex.h).
239 * For those who want to know, gcc will give a 64-bit result from a "*"
240 * operator if the result is a long long AND at least one of the
241 * operands is cast to long long (usually just prior to the "*" so as
242 * not to confuse it into thinking it really has a 64-bit operand,
243 * which, buy the way, it can do, but it takes more code and at least 2
246 * We also need to be aware that one second in nanoseconds is only a
247 * couple of bits away from overflowing a 32-bit word, so we MUST use
248 * 64-bits to get the full range time in nanoseconds.
253 * Here are the scales we will use. One for seconds, nanoseconds and
256 * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
257 * check if the sign bit is set. If not, we bump the shift count by 1.
258 * (Gets an extra bit of precision where we can use it.)
259 * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
260 * Haven't tested others.
262 * Limits of cpp (for #if expressions) only long (no long long), but
263 * then we only need the most signicant bit.
266 #define SEC_JIFFIE_SC (31 - SHIFT_HZ)
267 #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
269 #define SEC_JIFFIE_SC (32 - SHIFT_HZ)
271 #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
272 #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
273 #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
274 TICK_NSEC -1) / (u64)TICK_NSEC))
276 #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
277 TICK_NSEC -1) / (u64)TICK_NSEC))
278 #define USEC_CONVERSION \
279 ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
280 TICK_NSEC -1) / (u64)TICK_NSEC))
282 * USEC_ROUND is used in the timeval to jiffie conversion. See there
283 * for more details. It is the scaled resolution rounding value. Note
284 * that it is a 64-bit value. Since, when it is applied, we are already
285 * in jiffies (albit scaled), it is nothing but the bits we will shift
288 #define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
290 * The maximum jiffie value is (MAX_INT >> 1). Here we translate that
291 * into seconds. The 64-bit case will overflow if we are not careful,
292 * so use the messy SH_DIV macro to do it. Still all constants.
294 #if BITS_PER_LONG < 64
295 # define MAX_SEC_IN_JIFFIES \
296 (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
297 #else /* take care of overflow on 64 bits machines */
298 # define MAX_SEC_IN_JIFFIES \
299 (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
304 * Convert various time units to each other:
306 extern unsigned int jiffies_to_msecs(const unsigned long j);
307 extern unsigned int jiffies_to_usecs(const unsigned long j);
308 extern unsigned long msecs_to_jiffies(const unsigned int m);
309 extern unsigned long usecs_to_jiffies(const unsigned int u);
310 extern unsigned long timespec_to_jiffies(const struct timespec *value);
311 extern void jiffies_to_timespec(const unsigned long jiffies,
312 struct timespec *value);
313 extern unsigned long timeval_to_jiffies(const struct timeval *value);
314 extern void jiffies_to_timeval(const unsigned long jiffies,
315 struct timeval *value);
316 extern clock_t jiffies_to_clock_t(unsigned long x);
317 extern unsigned long clock_t_to_jiffies(unsigned long x);
318 extern u64 jiffies_64_to_clock_t(u64 x);
319 extern u64 nsec_to_clock_t(u64 x);
320 extern u64 nsecs_to_jiffies64(u64 n);
321 extern unsigned long nsecs_to_jiffies(u64 n);
323 #define TIMESTAMP_SIZE 30