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Diffstat (limited to 'kernel/include/linux/jiffies.h')
| -rw-r--r-- | kernel/include/linux/jiffies.h | 314 |
1 files changed, 314 insertions, 0 deletions
diff --git a/kernel/include/linux/jiffies.h b/kernel/include/linux/jiffies.h new file mode 100644 index 000000000..c367cbdf7 --- /dev/null +++ b/kernel/include/linux/jiffies.h @@ -0,0 +1,314 @@ +#ifndef _LINUX_JIFFIES_H +#define _LINUX_JIFFIES_H + +#include <linux/math64.h> +#include <linux/kernel.h> +#include <linux/types.h> +#include <linux/time.h> +#include <linux/timex.h> +#include <asm/param.h> /* for HZ */ + +/* + * The following defines establish the engineering parameters of the PLL + * model. The HZ variable establishes the timer interrupt frequency, 100 Hz + * for the SunOS kernel, 256 Hz for the Ultrix kernel and 1024 Hz for the + * OSF/1 kernel. The SHIFT_HZ define expresses the same value as the + * nearest power of two in order to avoid hardware multiply operations. + */ +#if HZ >= 12 && HZ < 24 +# define SHIFT_HZ 4 +#elif HZ >= 24 && HZ < 48 +# define SHIFT_HZ 5 +#elif HZ >= 48 && HZ < 96 +# define SHIFT_HZ 6 +#elif HZ >= 96 && HZ < 192 +# define SHIFT_HZ 7 +#elif HZ >= 192 && HZ < 384 +# define SHIFT_HZ 8 +#elif HZ >= 384 && HZ < 768 +# define SHIFT_HZ 9 +#elif HZ >= 768 && HZ < 1536 +# define SHIFT_HZ 10 +#elif HZ >= 1536 && HZ < 3072 +# define SHIFT_HZ 11 +#elif HZ >= 3072 && HZ < 6144 +# define SHIFT_HZ 12 +#elif HZ >= 6144 && HZ < 12288 +# define SHIFT_HZ 13 +#else +# error Invalid value of HZ. +#endif + +/* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can + * improve accuracy by shifting LSH bits, hence calculating: + * (NOM << LSH) / DEN + * This however means trouble for large NOM, because (NOM << LSH) may no + * longer fit in 32 bits. The following way of calculating this gives us + * some slack, under the following conditions: + * - (NOM / DEN) fits in (32 - LSH) bits. + * - (NOM % DEN) fits in (32 - LSH) bits. + */ +#define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \ + + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN)) + +/* LATCH is used in the interval timer and ftape setup. */ +#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */ + +extern int register_refined_jiffies(long clock_tick_rate); + +/* TICK_NSEC is the time between ticks in nsec assuming SHIFTED_HZ */ +#define TICK_NSEC ((NSEC_PER_SEC+HZ/2)/HZ) + +/* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */ +#define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ) + +/* some arch's have a small-data section that can be accessed register-relative + * but that can only take up to, say, 4-byte variables. jiffies being part of + * an 8-byte variable may not be correctly accessed unless we force the issue + */ +#define __jiffy_data __attribute__((section(".data"))) + +/* + * The 64-bit value is not atomic - you MUST NOT read it + * without sampling the sequence number in jiffies_lock. + * get_jiffies_64() will do this for you as appropriate. + */ +extern u64 __jiffy_data jiffies_64; +extern unsigned long volatile __jiffy_data jiffies; + +#if (BITS_PER_LONG < 64) +u64 get_jiffies_64(void); +#else +static inline u64 get_jiffies_64(void) +{ + return (u64)jiffies; +} +#endif + +/* + * These inlines deal with timer wrapping correctly. You are + * strongly encouraged to use them + * 1. Because people otherwise forget + * 2. Because if the timer wrap changes in future you won't have to + * alter your driver code. + * + * time_after(a,b) returns true if the time a is after time b. + * + * Do this with "<0" and ">=0" to only test the sign of the result. A + * good compiler would generate better code (and a really good compiler + * wouldn't care). Gcc is currently neither. + */ +#define time_after(a,b) \ + (typecheck(unsigned long, a) && \ + typecheck(unsigned long, b) && \ + ((long)((b) - (a)) < 0)) +#define time_before(a,b) time_after(b,a) + +#define time_after_eq(a,b) \ + (typecheck(unsigned long, a) && \ + typecheck(unsigned long, b) && \ + ((long)((a) - (b)) >= 0)) +#define time_before_eq(a,b) time_after_eq(b,a) + +/* + * Calculate whether a is in the range of [b, c]. + */ +#define time_in_range(a,b,c) \ + (time_after_eq(a,b) && \ + time_before_eq(a,c)) + +/* + * Calculate whether a is in the range of [b, c). + */ +#define time_in_range_open(a,b,c) \ + (time_after_eq(a,b) && \ + time_before(a,c)) + +/* Same as above, but does so with platform independent 64bit types. + * These must be used when utilizing jiffies_64 (i.e. return value of + * get_jiffies_64() */ +#define time_after64(a,b) \ + (typecheck(__u64, a) && \ + typecheck(__u64, b) && \ + ((__s64)((b) - (a)) < 0)) +#define time_before64(a,b) time_after64(b,a) + +#define time_after_eq64(a,b) \ + (typecheck(__u64, a) && \ + typecheck(__u64, b) && \ + ((__s64)((a) - (b)) >= 0)) +#define time_before_eq64(a,b) time_after_eq64(b,a) + +#define time_in_range64(a, b, c) \ + (time_after_eq64(a, b) && \ + time_before_eq64(a, c)) + +/* + * These four macros compare jiffies and 'a' for convenience. + */ + +/* time_is_before_jiffies(a) return true if a is before jiffies */ +#define time_is_before_jiffies(a) time_after(jiffies, a) + +/* time_is_after_jiffies(a) return true if a is after jiffies */ +#define time_is_after_jiffies(a) time_before(jiffies, a) + +/* time_is_before_eq_jiffies(a) return true if a is before or equal to jiffies*/ +#define time_is_before_eq_jiffies(a) time_after_eq(jiffies, a) + +/* time_is_after_eq_jiffies(a) return true if a is after or equal to jiffies*/ +#define time_is_after_eq_jiffies(a) time_before_eq(jiffies, a) + +/* + * Have the 32 bit jiffies value wrap 5 minutes after boot + * so jiffies wrap bugs show up earlier. + */ +#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ)) + +/* + * Change timeval to jiffies, trying to avoid the + * most obvious overflows.. + * + * And some not so obvious. + * + * Note that we don't want to return LONG_MAX, because + * for various timeout reasons we often end up having + * to wait "jiffies+1" in order to guarantee that we wait + * at _least_ "jiffies" - so "jiffies+1" had better still + * be positive. + */ +#define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1) + +extern unsigned long preset_lpj; + +/* + * We want to do realistic conversions of time so we need to use the same + * values the update wall clock code uses as the jiffies size. This value + * is: TICK_NSEC (which is defined in timex.h). This + * is a constant and is in nanoseconds. We will use scaled math + * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and + * NSEC_JIFFIE_SC. Note that these defines contain nothing but + * constants and so are computed at compile time. SHIFT_HZ (computed in + * timex.h) adjusts the scaling for different HZ values. + + * Scaled math??? What is that? + * + * Scaled math is a way to do integer math on values that would, + * otherwise, either overflow, underflow, or cause undesired div + * instructions to appear in the execution path. In short, we "scale" + * up the operands so they take more bits (more precision, less + * underflow), do the desired operation and then "scale" the result back + * by the same amount. If we do the scaling by shifting we avoid the + * costly mpy and the dastardly div instructions. + + * Suppose, for example, we want to convert from seconds to jiffies + * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The + * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We + * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we + * might calculate at compile time, however, the result will only have + * about 3-4 bits of precision (less for smaller values of HZ). + * + * So, we scale as follows: + * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE); + * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE; + * Then we make SCALE a power of two so: + * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE; + * Now we define: + * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) + * jiff = (sec * SEC_CONV) >> SCALE; + * + * Often the math we use will expand beyond 32-bits so we tell C how to + * do this and pass the 64-bit result of the mpy through the ">> SCALE" + * which should take the result back to 32-bits. We want this expansion + * to capture as much precision as possible. At the same time we don't + * want to overflow so we pick the SCALE to avoid this. In this file, + * that means using a different scale for each range of HZ values (as + * defined in timex.h). + * + * For those who want to know, gcc will give a 64-bit result from a "*" + * operator if the result is a long long AND at least one of the + * operands is cast to long long (usually just prior to the "*" so as + * not to confuse it into thinking it really has a 64-bit operand, + * which, buy the way, it can do, but it takes more code and at least 2 + * mpys). + + * We also need to be aware that one second in nanoseconds is only a + * couple of bits away from overflowing a 32-bit word, so we MUST use + * 64-bits to get the full range time in nanoseconds. + + */ + +/* + * Here are the scales we will use. One for seconds, nanoseconds and + * microseconds. + * + * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and + * check if the sign bit is set. If not, we bump the shift count by 1. + * (Gets an extra bit of precision where we can use it.) + * We know it is set for HZ = 1024 and HZ = 100 not for 1000. + * Haven't tested others. + + * Limits of cpp (for #if expressions) only long (no long long), but + * then we only need the most signicant bit. + */ + +#define SEC_JIFFIE_SC (31 - SHIFT_HZ) +#if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000) +#undef SEC_JIFFIE_SC +#define SEC_JIFFIE_SC (32 - SHIFT_HZ) +#endif +#define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29) +#define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\ + TICK_NSEC -1) / (u64)TICK_NSEC)) + +#define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\ + TICK_NSEC -1) / (u64)TICK_NSEC)) +/* + * The maximum jiffie value is (MAX_INT >> 1). Here we translate that + * into seconds. The 64-bit case will overflow if we are not careful, + * so use the messy SH_DIV macro to do it. Still all constants. + */ +#if BITS_PER_LONG < 64 +# define MAX_SEC_IN_JIFFIES \ + (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC) +#else /* take care of overflow on 64 bits machines */ +# define MAX_SEC_IN_JIFFIES \ + (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1) + +#endif + +/* + * Convert various time units to each other: + */ +extern unsigned int jiffies_to_msecs(const unsigned long j); +extern unsigned int jiffies_to_usecs(const unsigned long j); + +static inline u64 jiffies_to_nsecs(const unsigned long j) +{ + return (u64)jiffies_to_usecs(j) * NSEC_PER_USEC; +} + +extern unsigned long msecs_to_jiffies(const unsigned int m); +extern unsigned long usecs_to_jiffies(const unsigned int u); +extern unsigned long timespec_to_jiffies(const struct timespec *value); +extern void jiffies_to_timespec(const unsigned long jiffies, + struct timespec *value); +extern unsigned long timeval_to_jiffies(const struct timeval *value); +extern void jiffies_to_timeval(const unsigned long jiffies, + struct timeval *value); + +extern clock_t jiffies_to_clock_t(unsigned long x); +static inline clock_t jiffies_delta_to_clock_t(long delta) +{ + return jiffies_to_clock_t(max(0L, delta)); +} + +extern unsigned long clock_t_to_jiffies(unsigned long x); +extern u64 jiffies_64_to_clock_t(u64 x); +extern u64 nsec_to_clock_t(u64 x); +extern u64 nsecs_to_jiffies64(u64 n); +extern unsigned long nsecs_to_jiffies(u64 n); + +#define TIMESTAMP_SIZE 30 + +#endif |