linux-kernel - [RFC patch] reset TSC at the begining of check_tsc

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Message-ID: <3877989d0906010201j438a08a8x559f62b0aed40696@mail.gmail.com>
Date:	Mon, 1 Jun 2009 17:01:53 +0800
From:	Luming Yu <luming.yu@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: [RFC patch] reset TSC at the begining of check_tsc_warp

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@...el.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();

Download attachment "2.patch" of type "application/octet-stream" (360 bytes)