#ifndef _LINUX_JIFFIES_H #define _LINUX_JIFFIES_H #include #include #include #include #include #include /* 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 #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 <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) return (MSEC_PER_SEC / HZ) * j; #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); #else return (j * MSEC_PER_SEC) / HZ; #endif } static inline unsigned int jiffies_to_usecs(const unsigned long j) { #if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) return (USEC_PER_SEC / HZ) * j; #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC); #else return (j * USEC_PER_SEC) / 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 <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ) return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ); #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC) return m * (HZ / MSEC_PER_SEC); #else return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC; #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 <= USEC_PER_SEC && !(USEC_PER_SEC % HZ) return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ); #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC) return u * (HZ / USEC_PER_SEC); #else return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC; #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; long tv_usec; value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tv_usec); tv_usec /= NSEC_PER_USEC; value->tv_usec = tv_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