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From: Pallipadi, Venkatesh on 1 Mar 2010 13:00

Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi(a)intel.com>

On Mon, 2010-03-01 at 09:48 -0800, Dimitri Sivanich wrote:
> 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(a)sgi.com>
>
> ---
>
> 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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Prev: [PATCH 2/2] x86-32: fix atomic64_inc_not_zero return value convention
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