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jiffies.h
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1 #ifndef _LINUX_JIFFIES_H
2 #define _LINUX_JIFFIES_H
3 
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 */
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 #elif HZ >= 1536 && HZ < 3072
33 # define SHIFT_HZ 11
34 #elif HZ >= 3072 && HZ < 6144
35 # define SHIFT_HZ 12
36 #elif HZ >= 6144 && HZ < 12288
37 # define SHIFT_HZ 13
38 #else
39 # error Invalid value of HZ.
40 #endif
41 
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:
44  * (NOM << LSH) / DEN
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.
50  */
51 #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \
52  + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
53 
54 /* LATCH is used in the interval timer and ftape setup. */
55 #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */
56 
57 extern int register_refined_jiffies(long clock_tick_rate);
58 
59 /* TICK_NSEC is the time between ticks in nsec assuming SHIFTED_HZ */
60 #define TICK_NSEC ((NSEC_PER_SEC+HZ/2)/HZ)
61 
62 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
63 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
64 
65 /* some arch's have a small-data section that can be accessed register-relative
66  * but that can only take up to, say, 4-byte variables. jiffies being part of
67  * an 8-byte variable may not be correctly accessed unless we force the issue
68  */
69 #define __jiffy_data __attribute__((section(".data")))
70 
71 /*
72  * The 64-bit value is not atomic - you MUST NOT read it
73  * without sampling the sequence number in xtime_lock.
74  * get_jiffies_64() will do this for you as appropriate.
75  */
77 extern unsigned long volatile __jiffy_data jiffies;
78 
79 #if (BITS_PER_LONG < 64)
80 u64 get_jiffies_64(void);
81 #else
82 static inline u64 get_jiffies_64(void)
83 {
84  return (u64)jiffies;
85 }
86 #endif
87 
88 /*
89  * These inlines deal with timer wrapping correctly. You are
90  * strongly encouraged to use them
91  * 1. Because people otherwise forget
92  * 2. Because if the timer wrap changes in future you won't have to
93  * alter your driver code.
94  *
95  * time_after(a,b) returns true if the time a is after time b.
96  *
97  * Do this with "<0" and ">=0" to only test the sign of the result. A
98  * good compiler would generate better code (and a really good compiler
99  * wouldn't care). Gcc is currently neither.
100  */
101 #define time_after(a,b) \
102  (typecheck(unsigned long, a) && \
103  typecheck(unsigned long, b) && \
104  ((long)(b) - (long)(a) < 0))
105 #define time_before(a,b) time_after(b,a)
106 
107 #define time_after_eq(a,b) \
108  (typecheck(unsigned long, a) && \
109  typecheck(unsigned long, b) && \
110  ((long)(a) - (long)(b) >= 0))
111 #define time_before_eq(a,b) time_after_eq(b,a)
112 
113 /*
114  * Calculate whether a is in the range of [b, c].
115  */
116 #define time_in_range(a,b,c) \
117  (time_after_eq(a,b) && \
118  time_before_eq(a,c))
119 
120 /*
121  * Calculate whether a is in the range of [b, c).
122  */
123 #define time_in_range_open(a,b,c) \
124  (time_after_eq(a,b) && \
125  time_before(a,c))
126 
127 /* Same as above, but does so with platform independent 64bit types.
128  * These must be used when utilizing jiffies_64 (i.e. return value of
129  * get_jiffies_64() */
130 #define time_after64(a,b) \
131  (typecheck(__u64, a) && \
132  typecheck(__u64, b) && \
133  ((__s64)(b) - (__s64)(a) < 0))
134 #define time_before64(a,b) time_after64(b,a)
135 
136 #define time_after_eq64(a,b) \
137  (typecheck(__u64, a) && \
138  typecheck(__u64, b) && \
139  ((__s64)(a) - (__s64)(b) >= 0))
140 #define time_before_eq64(a,b) time_after_eq64(b,a)
141 
142 /*
143  * These four macros compare jiffies and 'a' for convenience.
144  */
145 
146 /* time_is_before_jiffies(a) return true if a is before jiffies */
147 #define time_is_before_jiffies(a) time_after(jiffies, a)
148 
149 /* time_is_after_jiffies(a) return true if a is after jiffies */
150 #define time_is_after_jiffies(a) time_before(jiffies, a)
151 
152 /* time_is_before_eq_jiffies(a) return true if a is before or equal to jiffies*/
153 #define time_is_before_eq_jiffies(a) time_after_eq(jiffies, a)
154 
155 /* time_is_after_eq_jiffies(a) return true if a is after or equal to jiffies*/
156 #define time_is_after_eq_jiffies(a) time_before_eq(jiffies, a)
157 
158 /*
159  * Have the 32 bit jiffies value wrap 5 minutes after boot
160  * so jiffies wrap bugs show up earlier.
161  */
162 #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
163 
164 /*
165  * Change timeval to jiffies, trying to avoid the
166  * most obvious overflows..
167  *
168  * And some not so obvious.
169  *
170  * Note that we don't want to return LONG_MAX, because
171  * for various timeout reasons we often end up having
172  * to wait "jiffies+1" in order to guarantee that we wait
173  * at _least_ "jiffies" - so "jiffies+1" had better still
174  * be positive.
175  */
176 #define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1)
177 
178 extern unsigned long preset_lpj;
179 
180 /*
181  * We want to do realistic conversions of time so we need to use the same
182  * values the update wall clock code uses as the jiffies size. This value
183  * is: TICK_NSEC (which is defined in timex.h). This
184  * is a constant and is in nanoseconds. We will use scaled math
185  * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and
186  * NSEC_JIFFIE_SC. Note that these defines contain nothing but
187  * constants and so are computed at compile time. SHIFT_HZ (computed in
188  * timex.h) adjusts the scaling for different HZ values.
189 
190  * Scaled math??? What is that?
191  *
192  * Scaled math is a way to do integer math on values that would,
193  * otherwise, either overflow, underflow, or cause undesired div
194  * instructions to appear in the execution path. In short, we "scale"
195  * up the operands so they take more bits (more precision, less
196  * underflow), do the desired operation and then "scale" the result back
197  * by the same amount. If we do the scaling by shifting we avoid the
198  * costly mpy and the dastardly div instructions.
199 
200  * Suppose, for example, we want to convert from seconds to jiffies
201  * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The
202  * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We
203  * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we
204  * might calculate at compile time, however, the result will only have
205  * about 3-4 bits of precision (less for smaller values of HZ).
206  *
207  * So, we scale as follows:
208  * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE);
209  * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE;
210  * Then we make SCALE a power of two so:
211  * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE;
212  * Now we define:
213  * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE))
214  * jiff = (sec * SEC_CONV) >> SCALE;
215  *
216  * Often the math we use will expand beyond 32-bits so we tell C how to
217  * do this and pass the 64-bit result of the mpy through the ">> SCALE"
218  * which should take the result back to 32-bits. We want this expansion
219  * to capture as much precision as possible. At the same time we don't
220  * want to overflow so we pick the SCALE to avoid this. In this file,
221  * that means using a different scale for each range of HZ values (as
222  * defined in timex.h).
223  *
224  * For those who want to know, gcc will give a 64-bit result from a "*"
225  * operator if the result is a long long AND at least one of the
226  * operands is cast to long long (usually just prior to the "*" so as
227  * not to confuse it into thinking it really has a 64-bit operand,
228  * which, buy the way, it can do, but it takes more code and at least 2
229  * mpys).
230 
231  * We also need to be aware that one second in nanoseconds is only a
232  * couple of bits away from overflowing a 32-bit word, so we MUST use
233  * 64-bits to get the full range time in nanoseconds.
234 
235  */
236 
237 /*
238  * Here are the scales we will use. One for seconds, nanoseconds and
239  * microseconds.
240  *
241  * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and
242  * check if the sign bit is set. If not, we bump the shift count by 1.
243  * (Gets an extra bit of precision where we can use it.)
244  * We know it is set for HZ = 1024 and HZ = 100 not for 1000.
245  * Haven't tested others.
246 
247  * Limits of cpp (for #if expressions) only long (no long long), but
248  * then we only need the most signicant bit.
249  */
250 
251 #define SEC_JIFFIE_SC (31 - SHIFT_HZ)
252 #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000)
253 #undef SEC_JIFFIE_SC
254 #define SEC_JIFFIE_SC (32 - SHIFT_HZ)
255 #endif
256 #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29)
257 #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19)
258 #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\
259  TICK_NSEC -1) / (u64)TICK_NSEC))
260 
261 #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\
262  TICK_NSEC -1) / (u64)TICK_NSEC))
263 #define USEC_CONVERSION \
264  ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\
265  TICK_NSEC -1) / (u64)TICK_NSEC))
266 /*
267  * USEC_ROUND is used in the timeval to jiffie conversion. See there
268  * for more details. It is the scaled resolution rounding value. Note
269  * that it is a 64-bit value. Since, when it is applied, we are already
270  * in jiffies (albit scaled), it is nothing but the bits we will shift
271  * off.
272  */
273 #define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1)
274 /*
275  * The maximum jiffie value is (MAX_INT >> 1). Here we translate that
276  * into seconds. The 64-bit case will overflow if we are not careful,
277  * so use the messy SH_DIV macro to do it. Still all constants.
278  */
279 #if BITS_PER_LONG < 64
280 # define MAX_SEC_IN_JIFFIES \
281  (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC)
282 #else /* take care of overflow on 64 bits machines */
283 # define MAX_SEC_IN_JIFFIES \
284  (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
285 
286 #endif
287 
288 /*
289  * Convert various time units to each other:
290  */
291 extern unsigned int jiffies_to_msecs(const unsigned long j);
292 extern unsigned int jiffies_to_usecs(const unsigned long j);
293 extern unsigned long msecs_to_jiffies(const unsigned int m);
294 extern unsigned long usecs_to_jiffies(const unsigned int u);
295 extern unsigned long timespec_to_jiffies(const struct timespec *value);
296 extern void jiffies_to_timespec(const unsigned long jiffies,
297  struct timespec *value);
298 extern unsigned long timeval_to_jiffies(const struct timeval *value);
299 extern void jiffies_to_timeval(const unsigned long jiffies,
300  struct timeval *value);
301 
302 extern clock_t jiffies_to_clock_t(unsigned long x);
303 static inline clock_t jiffies_delta_to_clock_t(long delta)
304 {
305  return jiffies_to_clock_t(max(0L, delta));
306 }
307 
308 extern unsigned long clock_t_to_jiffies(unsigned long x);
310 extern u64 nsec_to_clock_t(u64 x);
311 extern u64 nsecs_to_jiffies64(u64 n);
312 extern unsigned long nsecs_to_jiffies(u64 n);
313 
314 #define TIMESTAMP_SIZE 30
315 
316 #endif