From dacb16b1a034fa7a0b868ee30758119fbfd90bc1 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Sun, 30 Oct 2005 14:59:25 -0800 Subject: [PATCH] i386 and x86_64 TSC set_cyc2ns_scale imprecision I just found out that some precision is unnecessarily lost in the arch/i386/kernel/timers/timer_tsc.c:set_cyc2ns_scale function. It uses a cpu_mhz parameter when it could use a cpu_khz. In the specific case of an Intel P4 running at 3001.171 Mhz, the truncation to 3001 Mhz leads to an imprecision of 19 microseconds per second : this is very sad for a timer with nearly nanosecond accuracy. Fix the x86_64 architecture too. Cc: george anzinger Cc: john stultz Cc: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/x86_64/kernel/time.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'arch/x86_64/kernel') diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c index 703acde2a1a..47d25ad0816 100644 --- a/arch/x86_64/kernel/time.c +++ b/arch/x86_64/kernel/time.c @@ -481,9 +481,9 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) static unsigned int cyc2ns_scale; #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */ -static inline void set_cyc2ns_scale(unsigned long cpu_mhz) +static inline void set_cyc2ns_scale(unsigned long cpu_khz) { - cyc2ns_scale = (1000 << CYC2NS_SCALE_FACTOR)/cpu_mhz; + cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz; } static inline unsigned long long cycles_2_ns(unsigned long long cyc) @@ -655,7 +655,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, vxtime.tsc_quot = (1000L << 32) / cpu_khz; } - set_cyc2ns_scale(cpu_khz_ref / 1000); + set_cyc2ns_scale(cpu_khz_ref); return 0; } @@ -939,7 +939,7 @@ void __init time_init(void) rdtscll_sync(&vxtime.last_tsc); setup_irq(0, &irq0); - set_cyc2ns_scale(cpu_khz / 1000); + set_cyc2ns_scale(cpu_khz); #ifndef CONFIG_SMP time_init_gtod(); -- cgit v1.2.3