[PATCH v2] x86: Fix sched_clock_cpu for systems withunsynchronized TSC

[Dimitri Sivanich]

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@xxxxxxx>

---

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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