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Diffstat (limited to 'include/linux/jiffies.h')
| -rw-r--r-- | include/linux/jiffies.h | 450 |
1 files changed, 450 insertions, 0 deletions
diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h new file mode 100644 index 00000000000..d7a2555a886 --- /dev/null +++ b/include/linux/jiffies.h @@ -0,0 +1,450 @@ +#ifndef _LINUX_JIFFIES_H +#define _LINUX_JIFFIES_H + +#include <linux/kernel.h> +#include <linux/types.h> +#include <linux/time.h> +#include <linux/timex.h> +#include <asm/param.h> /* for HZ */ +#include <asm/div64.h> + +#ifndef div_long_long_rem +#define div_long_long_rem(dividend,divisor,remainder) \ +({ \ + u64 result = dividend; \ + *remainder = do_div(result,divisor); \ + result; \ +}) +#endif + +/* + * 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 +#else +# error You lose. +#endif + +/* LATCH is used in the interval timer and ftape setup. */ +#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */ + +/* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, the 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) + +/* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */ +#define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8)) + +/* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */ +#define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8)) + +/* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */ +#define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ) + +/* TICK_USEC_TO_NSEC is the time between ticks in nsec assuming real ACTHZ and */ +/* a value TUSEC for TICK_USEC (can be set bij adjtimex) */ +#define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8)) + +/* 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 volatile - you MUST NOT read it + * without sampling the sequence number in xtime_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) - (long)(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) - (long)(b) >= 0)) +#define time_before_eq(a,b) time_after_eq(b,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 MAX_LONG, 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 ((~0UL >> 1)-1) + +/* + * 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 used 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 take 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 USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19) +#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)) +#define USEC_CONVERSION \ + ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\ + TICK_NSEC -1) / (u64)TICK_NSEC)) +/* + * USEC_ROUND is used in the timeval to jiffie conversion. See there + * for more details. It is the scaled resolution rounding value. Note + * that it is a 64-bit value. Since, when it is applied, we are already + * in jiffies (albit scaled), it is nothing but the bits we will shift + * off. + */ +#define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1) +/* + * 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 jiffies to milliseconds and back. + * + * Avoid unnecessary multiplications/divisions in the + * two most common HZ cases: + */ +static inline unsigned int jiffies_to_msecs(const unsigned long j) +{ +#if HZ <= 1000 && !(1000 % HZ) + return (1000 / HZ) * j; +#elif HZ > 1000 && !(HZ % 1000) + return (j + (HZ / 1000) - 1)/(HZ / 1000); +#else + return (j * 1000) / HZ; +#endif +} + +static inline unsigned int jiffies_to_usecs(const unsigned long j) +{ +#if HZ <= 1000000 && !(1000000 % HZ) + return (1000000 / HZ) * j; +#elif HZ > 1000000 && !(HZ % 1000000) + return (j + (HZ / 1000000) - 1)/(HZ / 1000000); +#else + return (j * 1000000) / HZ; +#endif +} + +static inline unsigned long msecs_to_jiffies(const unsigned int m) +{ + if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET)) + return MAX_JIFFY_OFFSET; +#if HZ <= 1000 && !(1000 % HZ) + return (m + (1000 / HZ) - 1) / (1000 / HZ); +#elif HZ > 1000 && !(HZ % 1000) + return m * (HZ / 1000); +#else + return (m * HZ + 999) / 1000; +#endif +} + +static inline unsigned long usecs_to_jiffies(const unsigned int u) +{ + if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET)) + return MAX_JIFFY_OFFSET; +#if HZ <= 1000000 && !(1000000 % HZ) + return (u + (1000000 / HZ) - 1) / (1000000 / HZ); +#elif HZ > 1000000 && !(HZ % 1000000) + return u * (HZ / 1000000); +#else + return (u * HZ + 999999) / 1000000; +#endif +} + +/* + * The TICK_NSEC - 1 rounds up the value to the next resolution. Note + * that a remainder subtract here would not do the right thing as the + * resolution values don't fall on second boundries. I.e. the line: + * nsec -= nsec % TICK_NSEC; is NOT a correct resolution rounding. + * + * Rather, we just shift the bits off the right. + * + * The >> (NSEC_JIFFIE_SC - SEC_JIFFIE_SC) converts the scaled nsec + * value to a scaled second value. + */ +static __inline__ unsigned long +timespec_to_jiffies(const struct timespec *value) +{ + unsigned long sec = value->tv_sec; + long nsec = value->tv_nsec + TICK_NSEC - 1; + + if (sec >= MAX_SEC_IN_JIFFIES){ + sec = MAX_SEC_IN_JIFFIES; + nsec = 0; + } + return (((u64)sec * SEC_CONVERSION) + + (((u64)nsec * NSEC_CONVERSION) >> + (NSEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; + +} + +static __inline__ void +jiffies_to_timespec(const unsigned long jiffies, struct timespec *value) +{ + /* + * Convert jiffies to nanoseconds and separate with + * one divide. + */ + u64 nsec = (u64)jiffies * TICK_NSEC; + value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec); +} + +/* Same for "timeval" + * + * Well, almost. The problem here is that the real system resolution is + * in nanoseconds and the value being converted is in micro seconds. + * Also for some machines (those that use HZ = 1024, in-particular), + * there is a LARGE error in the tick size in microseconds. + + * The solution we use is to do the rounding AFTER we convert the + * microsecond part. Thus the USEC_ROUND, the bits to be shifted off. + * Instruction wise, this should cost only an additional add with carry + * instruction above the way it was done above. + */ +static __inline__ unsigned long +timeval_to_jiffies(const struct timeval *value) +{ + unsigned long sec = value->tv_sec; + long usec = value->tv_usec; + + if (sec >= MAX_SEC_IN_JIFFIES){ + sec = MAX_SEC_IN_JIFFIES; + usec = 0; + } + return (((u64)sec * SEC_CONVERSION) + + (((u64)usec * USEC_CONVERSION + USEC_ROUND) >> + (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; +} + +static __inline__ void +jiffies_to_timeval(const unsigned long jiffies, struct timeval *value) +{ + /* + * Convert jiffies to nanoseconds and separate with + * one divide. + */ + u64 nsec = (u64)jiffies * TICK_NSEC; + value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_usec); + value->tv_usec /= NSEC_PER_USEC; +} + +/* + * Convert jiffies/jiffies_64 to clock_t and back. + */ +static inline clock_t jiffies_to_clock_t(long x) +{ +#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 + return x / (HZ / USER_HZ); +#else + u64 tmp = (u64)x * TICK_NSEC; + do_div(tmp, (NSEC_PER_SEC / USER_HZ)); + return (long)tmp; +#endif +} + +static inline unsigned long clock_t_to_jiffies(unsigned long x) +{ +#if (HZ % USER_HZ)==0 + if (x >= ~0UL / (HZ / USER_HZ)) + return ~0UL; + return x * (HZ / USER_HZ); +#else + u64 jif; + + /* Don't worry about loss of precision here .. */ + if (x >= ~0UL / HZ * USER_HZ) + return ~0UL; + + /* .. but do try to contain it here */ + jif = x * (u64) HZ; + do_div(jif, USER_HZ); + return jif; +#endif +} + +static inline u64 jiffies_64_to_clock_t(u64 x) +{ +#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0 + do_div(x, HZ / USER_HZ); +#else + /* + * There are better ways that don't overflow early, + * but even this doesn't overflow in hundreds of years + * in 64 bits, so.. + */ + x *= TICK_NSEC; + do_div(x, (NSEC_PER_SEC / USER_HZ)); +#endif + return x; +} + +static inline u64 nsec_to_clock_t(u64 x) +{ +#if (NSEC_PER_SEC % USER_HZ) == 0 + do_div(x, (NSEC_PER_SEC / USER_HZ)); +#elif (USER_HZ % 512) == 0 + x *= USER_HZ/512; + do_div(x, (NSEC_PER_SEC / 512)); +#else + /* + * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024, + * overflow after 64.99 years. + * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ... + */ + x *= 9; + do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2)) + / USER_HZ)); +#endif + return x; +} + +#endif |