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This patch addresses issues of roundoff error in the time keeping and
NTP code as follows:
The conversion of "actual jiffies" to TICK_USEC and then to TICK_NSEC
introduced large errors if jiffies was not a power of 10 (e.g. 1024
for the ia64). Most of this is avoided by converting directly to
TICK_NSEC.
The calculation of MAX_SEC_IN_JIFFIES (the largest timespec or timeval
the kernel will attempt) had overflow problems in the 64-bit machines.
We introduce a different equation for those machines.
The NTP frequency update code was allowing a micro second of error to
accumulate before applying the correction. We change FINEUSEC to
FINENSEC to do the correction as soon as a full nanosecond has
accumulated.
The initial calculation of time_freq for NTP had severe roundoff
errors for HZ not a power of 10 (i.e. 1024). A new equation fixes this.
clock_nanosleep is changed to round up to the next jiffie to cover
starting between jiffies.
(Note, this patch depends on the prior timeclean up patch of this date.)
-- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml--=_courier-25031-1055203183-0001-2 Content-Type: text/plain; name="timeclean-eric-2.5.70-1.0.patch"; charset=iso-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="timeclean-eric-2.5.70-1.0.patch"
diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/arch/i386/kernel/time.c linux/arch/i386/kernel/time.c --- linux-2.5.70-time_save/arch/i386/kernel/time.c 2003-05-30 01:29:48.000000000 -0700 +++ linux/arch/i386/kernel/time.c 2003-06-09 16:23:04.000000000 -0700 @@ -127,7 +127,7 @@ * made, and then undo it! */ tv->tv_nsec -= timer->get_offset() * NSEC_PER_USEC; - tv->tv_nsec -= (jiffies - wall_jiffies) * TICK_NSEC(TICK_USEC); + tv->tv_nsec -= (jiffies - wall_jiffies) * TICK_NSEC; while (tv->tv_nsec < 0) { tv->tv_nsec += NSEC_PER_SEC; diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/include/asm-i386/mach-pc9800/setup_arch_pre.h linux/include/asm-i386/mach-pc9800/setup_arch_pre.h --- linux-2.5.70-time_save/include/asm-i386/mach-pc9800/setup_arch_pre.h 2003-03-24 23:34:12.000000000 -0800 +++ linux/include/asm-i386/mach-pc9800/setup_arch_pre.h 2003-06-09 16:03:59.000000000 -0700 @@ -26,7 +26,7 @@ CLOCK_TICK_RATE = PC9800_8MHz_P() ? 1996800 : 2457600; printk(KERN_DEBUG "CLOCK_TICK_RATE = %d\n", CLOCK_TICK_RATE); tick_usec = TICK_USEC; /* ACTHZ period (usec) */ - tick_nsec = TICK_NSEC(TICK_USEC); /* USER_HZ period (nsec) */ + tick_nsec = TICK_NSEC; /* USER_HZ period (nsec) */ pc9800_misc_flags = PC9800_MISC_FLAGS; #ifdef CONFIG_SMP diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/include/asm-ia64/timex.h linux/include/asm-ia64/timex.h --- linux-2.5.70-time_save/include/asm-ia64/timex.h 2002-09-26 11:24:18.000000000 -0700 +++ linux/include/asm-ia64/timex.h 2003-06-09 16:03:59.000000000 -0700 @@ -14,7 +14,11 @@ typedef unsigned long cycles_t; -#define CLOCK_TICK_RATE 100000000 +/* + * Something low processor frequency like 100Mhz but + * yet multiple of HZ to avoid truncation in some formulas. + */ +#define CLOCK_TICK_RATE (HZ * 100000UL) static inline cycles_t get_cycles (void) diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/include/linux/time.h linux/include/linux/time.h --- linux-2.5.70-time_save/include/linux/time.h 2003-05-30 01:29:48.000000000 -0700 +++ linux/include/linux/time.h 2003-06-09 16:03:59.000000000 -0700 @@ -69,10 +69,11 @@ #ifndef NSEC_PER_USEC #define NSEC_PER_USEC (1000L) #endif + /* * We want to do realistic conversions of time so we need to use the same * values the update wall clock code uses as the jiffie size. This value - * is: TICK_NSEC(TICK_USEC) (both of which are defined in timex.h). This + * is: TICK_NSEC (both of which are defined in timex.h). This * is a constant and is in nanoseconds. We will used scaled math and * with a scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and * NSEC_JIFFIE_SC. Note that these defines contain nothing but @@ -83,23 +84,30 @@ #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 30) #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 20) #define SEC_CONVERSION ((unsigned long)(((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) /\ - (u64)TICK_NSEC(TICK_USEC))) -#define NSEC_CONVERSION ((unsigned long)(((u64)1 << NSEC_JIFFIE_SC) / \ - (u64)TICK_NSEC(TICK_USEC))) -#define USEC_CONVERSION \ - ((unsigned long)(((u64)NSEC_PER_USEC << USEC_JIFFIE_SC)/ \ - (u64)TICK_NSEC(TICK_USEC))) -#define MAX_SEC_IN_JIFFIES \ - (u32)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC(TICK_USEC)) / NSEC_PER_SEC) + (u64)TICK_NSEC)) +#define NSEC_CONVERSION ((unsigned long)(((u64)1 << NSEC_JIFFIE_SC) /\ + (u64)TICK_NSEC)) +#define USEC_CONVERSION ((unsigned long)(((u64)NSEC_PER_USEC << USEC_JIFFIE_SC)/\ + (u64)TICK_NSEC)) +#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 static __inline__ unsigned long timespec_to_jiffies(struct timespec *value) { unsigned long sec = value->tv_sec; - long nsec = value->tv_nsec + TICK_NSEC(TICK_USEC) - 1; + long nsec = value->tv_nsec + TICK_NSEC - 1; - if (sec >= MAX_SEC_IN_JIFFIES) - return MAX_JIFFY_OFFSET; + 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; @@ -113,7 +121,7 @@ * Convert jiffies to nanoseconds and seperate with * one divide. */ - u64 nsec = (u64)jiffies * TICK_NSEC(TICK_USEC); + u64 nsec = (u64)jiffies * TICK_NSEC; value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec); } @@ -122,10 +130,12 @@ timeval_to_jiffies(struct timeval *value) { unsigned long sec = value->tv_sec; - long usec = value->tv_usec + USEC_PER_SEC / HZ - 1; + long usec = value->tv_usec + TICK_USEC - 1; - if (sec >= MAX_SEC_IN_JIFFIES) - return MAX_JIFFY_OFFSET; + if (sec >= MAX_SEC_IN_JIFFIES){ + sec = MAX_SEC_IN_JIFFIES; + usec = 0; + } return (((u64)sec * SEC_CONVERSION) + (((u64)usec * USEC_CONVERSION) >> (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >> SEC_JIFFIE_SC; @@ -138,7 +148,7 @@ * Convert jiffies to nanoseconds and seperate with * one divide. */ - u64 nsec = (u64)jiffies * TICK_NSEC(TICK_USEC); + 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; } diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/include/linux/timex.h linux/include/linux/timex.h --- linux-2.5.70-time_save/include/linux/timex.h 2003-05-05 15:34:09.000000000 -0700 +++ linux/include/linux/timex.h 2003-06-09 16:03:59.000000000 -0700 @@ -99,19 +99,19 @@ * variable which serves as an extension to the low-order bits of the * system clock variable. The SHIFT_UPDATE define establishes the decimal * point of the time_offset variable which represents the current offset - * with respect to standard time. The FINEUSEC define represents 1 usec in + * with respect to standard time. The FINENSEC define represents 1 nsec in * scaled units. * * SHIFT_USEC defines the scaling (shift) of the time_freq and * time_tolerance variables, which represent the current frequency * offset and maximum frequency tolerance. * - * FINEUSEC is 1 us in SHIFT_UPDATE units of the time_phase variable. + * FINENSEC is 1 ns in SHIFT_UPDATE units of the time_phase variable. */ #define SHIFT_SCALE 22 /* phase scale (shift) */ #define SHIFT_UPDATE (SHIFT_KG + MAXTC) /* time offset scale (shift) */ #define SHIFT_USEC 16 /* frequency offset scale (shift) */ -#define FINEUSEC (1L << SHIFT_SCALE) /* 1 us in phase units */ +#define FINENSEC (1L << (SHIFT_SCALE - 10)) /* ~1 ns in phase units */ #define MAXPHASE 512000L /* max phase error (us) */ #define MAXFREQ (512L << SHIFT_USEC) /* max frequency error (ppm) */ @@ -159,7 +159,7 @@ * (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 onditions: + * some slack, under the following conditions: * - (NOM / DEN) fits in (32 - LSH) bits. * - (NOM % DEN) fits in (32 - LSH) bits. */ @@ -169,12 +169,16 @@ /* 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) +#define TICK_USEC ((TICK_NSEC + 1000UL/2) / 1000UL) -/* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ and */ +/* 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_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8)) +#define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8)) + #include <linux/time.h> /* diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/kernel/posix-timers.c linux/kernel/posix-timers.c --- linux-2.5.70-time_save/kernel/posix-timers.c 2003-06-09 13:26:30.000000000 -0700 +++ linux/kernel/posix-timers.c 2003-06-09 16:15:14.000000000 -0700 @@ -33,7 +33,7 @@ result; }) #endif -#define CLOCK_REALTIME_RES TICK_NSEC(TICK_USEC) // In nano seconds. +#define CLOCK_REALTIME_RES TICK_NSEC // In nano seconds. static inline u64 mpy_l_X_l_ll(unsigned long mpy1,unsigned long mpy2) { @@ -1201,7 +1201,7 @@ if (abs || !rq_time) { adjust_abs_time(&posix_clocks[which_clock], &t, abs, &rq_time); - // rq_time += (t.tv_sec || t.tv_nsec); + rq_time += (t.tv_sec || t.tv_nsec); } left = rq_time - get_jiffies_64(); @@ -1232,7 +1232,7 @@ if (abs) return -ERESTARTNOHAND; - left *= TICK_NSEC(TICK_USEC); + left *= TICK_NSEC; tsave->tv_sec = div_long_long_rem(left, NSEC_PER_SEC, &tsave->tv_nsec); diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/kernel/time.c linux/kernel/time.c --- linux-2.5.70-time_save/kernel/time.c 2003-05-30 01:29:48.000000000 -0700 +++ linux/kernel/time.c 2003-06-09 16:03:59.000000000 -0700 @@ -339,7 +339,7 @@ } /* txc->modes & ADJ_OFFSET */ if (txc->modes & ADJ_TICK) { tick_usec = txc->tick; - tick_nsec = TICK_NSEC(tick_usec); + tick_nsec = TICK_USEC_TO_NSEC(tick_usec); } } /* txc->modes */ leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0 diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.70-time_save/kernel/timer.c linux/kernel/timer.c --- linux-2.5.70-time_save/kernel/timer.c 2003-05-30 01:29:48.000000000 -0700 +++ linux/kernel/timer.c 2003-06-09 16:19:46.000000000 -0700 @@ -439,7 +439,7 @@ * Timekeeping variables */ unsigned long tick_usec = TICK_USEC; /* ACTHZ period (usec) */ -unsigned long tick_nsec = TICK_NSEC(TICK_USEC); /* USER_HZ period (nsec) */ +unsigned long tick_nsec = TICK_NSEC; /* USER_HZ period (nsec) */ /* * The current time @@ -469,7 +469,7 @@ long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */ long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */ long time_phase; /* phase offset (scaled us) */ -long time_freq = ((1000000 + HZ/2) % HZ - HZ/2) << SHIFT_USEC; +long time_freq = (((NSEC_PER_SEC + HZ/2) % HZ - HZ/2) << SHIFT_USEC) / NSEC_PER_USEC; /* frequency offset (scaled ppm)*/ long time_adj; /* tick adjust (scaled 1 / HZ) */ long time_reftime; /* time at last adjustment (s) */ @@ -631,12 +631,12 @@ * advance the tick more. */ time_phase += time_adj; - if (time_phase <= -FINEUSEC) { + if (time_phase <= -FINENSEC) { long ltemp = -time_phase >> (SHIFT_SCALE - 10); time_phase += ltemp << (SHIFT_SCALE - 10); xtime.tv_nsec -= ltemp; } - else if (time_phase >= FINEUSEC) { + else if (time_phase >= FINENSEC) { long ltemp = time_phase >> (SHIFT_SCALE - 10); time_phase -= ltemp << (SHIFT_SCALE - 10); xtime.tv_nsec += ltemp;
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