Messages in this thread Patch in this message | | | Date | Mon, 1 Mar 2010 11:48:15 -0600 | From | Dimitri Sivanich <> | Subject | [PATCH v2] x86: 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.
Only set sched_clock_stable if tsc has not been marked unstable.
Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
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Only affects x86 arch.
arch/x86/kernel/cpu/intel.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
Index: linux/arch/x86/kernel/cpu/intel.c =================================================================== --- linux.orig/arch/x86/kernel/cpu/intel.c +++ linux/arch/x86/kernel/cpu/intel.c @@ -70,7 +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; + if (!check_tsc_unstable()) + sched_clock_stable = 1; } /*
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