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Subject[153/156] x86: Fix sched_clock_cpu for systems with unsynchronized TSC
From: Dimitri Sivanich <sivanich@sgi.com>

commit 14be1f7454ea96ee614467a49cf018a1a383b189 upstream.

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>
Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100301174815.GC8224@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/kernel/cpu/intel.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/intel.c
+++ b/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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