[RFC patch] reset TSC at the begining of check_tsc_warp

[Luming Yu <luming.yu@gmail.com>]

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Hello,

Without this patch, we always get kernel warning that TSC warp between CPUs,
and TSC is marked unstable due to check_tsc_sync_source failed if the CPUs
have the problem of not-synced initial TSC.

It hurts CPUs with constant-tsc feature, but with unsynced initial TSC value...

The downside is we could break perfect synced TSC with this patch.
Please review, test and apply.

**The patch is enclosed in text attachment*
**Using web client to send the patch* *
**below is c&p just for review, please apply attached  patch*/

Thanks,
Luming



Signed-off-by: Yu Luming <luming.yu@intel.com>

 tsc_sync.c |    1 +
 1 file changed, 1 insertion(+)


diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index bf36328..190c1b0 100644
--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -46,6 +46,7 @@ static __cpuinit void check_tsc_warp(void)
 	cycles_t start, now, prev, end;
 	int i;

+	wrmsrl(MSR_IA32_TSC, 0);
 	rdtsc_barrier();
 	start = get_cycles();
 	rdtsc_barrier();

[-- Attachment #2: 2.patch --]
[-- Type: application/octet-stream, Size: 360 bytes --]

diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index bf36328..190c1b0 100644
--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -46,6 +46,7 @@ static __cpuinit void check_tsc_warp(void)
 	cycles_t start, now, prev, end;
 	int i;
 
+	wrmsrl(MSR_IA32_TSC, 0);
 	rdtsc_barrier();
 	start = get_cycles();
 	rdtsc_barrier();