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| author | Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | 2005-10-30 14:59:25 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-10-30 17:37:11 -0800 |
| commit | dacb16b1a034fa7a0b868ee30758119fbfd90bc1 (patch) | |
| tree | daaa631c9c6fa2ad011647fb3acd219784faf2e2 /arch/x86_64 | |
| parent | bfd51626cbf61cb23f787d8ff972ef0d5ddacc0b (diff) | |
| download | linux-dacb16b1a034fa7a0b868ee30758119fbfd90bc1.tar.bz2 | |
[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 <george@mvista.com>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch/x86_64')
| -rw-r--r-- | arch/x86_64/kernel/time.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c index 703acde2a1a5..47d25ad08160 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(); |