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Subject: RE: constant_tsc and TSC unstable
Date: Thu, 29 Nov 2007 15:29:49 -0800
Message-ID: <924EFEDD5F540B4284297C4DC59F3DEE2FAA12@orsmsx423.amr.corp.intel.com>
In-Reply-To: <20071129171142.56c7890a@tux.DEF.witbe.net>
Thread-Topic: constant_tsc and TSC unstable
Thread-Index: AcgypERhj0w4Ihm5Qp+GkObyB/q0OgAOuiIA
References: <20071129171142.56c7890a@tux.DEF.witbe.net>
From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
To: =?iso-2022-jp?B?UGF1bCBSb2xsYW5kICgbJEIlXSE8JWshJiVtJWklcxsoQik=?= 
	<rol@witbe.net>,
       "Linux Kernel" <linux-kernel@vger.kernel.org>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1304
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>-----Original Message-----
>From: linux-kernel-owner@vger.kernel.org 
>[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Paul 
>Rolland (???・???)
>Sent: Thursday, November 29, 2007 8:12 AM
>To: Linux Kernel
>Cc: rol@witbe.net
>Subject: constant_tsc and TSC unstable
>
>Hello,
>
>I've a machine with a Core2Duo CPU. /proc/cpuinfo reports the flag
>constant_tsc, but at boot time, I have the log :
>
>...
>Total of 2 processors activated (6919.15 BogoMIPS).
>ENABLING IO-APIC IRQs
>..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
>checking TSC synchronization [CPU#0 -> CPU#1]:
>Measured 3978592228 cycles TSC warp between CPUs, turning off 
>TSC clock.
>Marking TSC unstable due to: check_tsc_sync_source failed.
>Brought up 2 CPUs
>...
>
>This machine is running 2.6.23.1-21.fc7. I know I should 
>report to Fedora,
>but I was wondering if this is a bug or a feature ;)
>

TSCs on Core 2 Duo are supposed to be in sync unless CPU supports deep idle states like C2, C3. Can you send the full /proc/cpuinfo and full dmesg.

Thanks,
Venki 
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