From: Greg KH on
2.6.32-stable review patch. If anyone has any objections, please let us know.


From: Pallipadi, Venkatesh <venkatesh.pallipadi(a)>

commit 6c56ccecf05fafe100ab4ea94f6fccbf5ff00db7 upstream.

Commit 83ce4009 did the following change
If the TSC is constant and non-stop, also set it reliable.

But, there seems to be few systems that will end up with TSC warp across
sockets, depending on how the cpus come out of reset. Skipping TSC sync
test on such systems may result in time inconsistency later.

So, reenable TSC sync test even on constant and non-stop TSC systems.
Set, sched_clock_stable to 1 by default and reset it in
mark_tsc_unstable, if TSC sync fails.

This change still gives perf benefit mentioned in 83ce4009 for systems
where TSC is reliable.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi(a)>
Acked-by: Suresh Siddha <suresh.b.siddha(a)>
LKML-Reference: <20091217202702.GA18015(a)>
Signed-off-by: H. Peter Anvin <hpa(a)>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)>

arch/x86/kernel/cpu/intel.c | 1 -
arch/x86/kernel/tsc.c | 1 +
2 files changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -70,7 +70,6 @@ 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);
- set_cpu_cap(c, X86_FEATURE_TSC_RELIABLE);
sched_clock_stable = 1;

--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -763,6 +763,7 @@ void mark_tsc_unstable(char *reason)
if (!tsc_unstable) {
tsc_unstable = 1;
+ sched_clock_stable = 0;
printk(KERN_INFO "Marking TSC unstable due to %s\n", reason);
/* Change only the rating, when not registered */
if (clocksource_tsc.mult)

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