Messages in this thread Patch in this message | | | Date | Thu, 25 Feb 2010 12:36:43 -0600 | From | Dimitri Sivanich <> | Subject | [PATCH] Fix sched_clock_cpu for systems with unsynchronized TSC |
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On UV systems, the TSC is not synchronized across blades. The sched_clock_cpu() function is returning values that can go backwards (I've seen as much as 8 seconds) when switching between cpus.
As each cpu comes up, early_init_intel() will currently set the sched_clock_stable flag true. When mark_tsc_unstable() runs, it clears the flag, but this only occurs once (the first time a cpu comes up whose TSC is not synchronized with cpu 0). After this, early_init_intel() will set the flag again as the next cpu comes up.
This patch changes the logic to assume that the sched_clock is stable at first. From then on it is only cleared.
Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
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arch/x86/kernel/cpu/intel.c | 4 ++-- kernel/sched_clock.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-)
Index: linux/arch/x86/kernel/cpu/intel.c =================================================================== --- linux.orig/arch/x86/kernel/cpu/intel.c +++ linux/arch/x86/kernel/cpu/intel.c @@ -70,8 +70,8 @@ static void __cpuinit early_init_intel(s if (c->x86_power & (1 << 8)) { set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); - sched_clock_stable = 1; - } + } else + sched_clock_stable = 0; /* * There is a known erratum on Pentium III and Core Solo Index: linux/kernel/sched_clock.c =================================================================== --- linux.orig/kernel/sched_clock.c +++ linux/kernel/sched_clock.c @@ -45,7 +45,7 @@ unsigned long long __attribute__((weak)) static __read_mostly int sched_clock_running; #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK -__read_mostly int sched_clock_stable; +__read_mostly int sched_clock_stable = 1; struct sched_clock_data { u64 tick_raw;
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