linux-kernel - Re: [PATCH 0/2] Make the TSC safe to be used by gettimeofday().

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Message-ID: <Pine.LNX.4.64.0611141327020.13469@schroedinger.engr.sgi.com>
Date:	Tue, 14 Nov 2006 13:28:04 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Suleiman Souhlal <ssouhlal@...ebsd.org>
cc:	Andi Kleen <ak@...e.de>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	vojtech@...e.cz, Jiri Bohac <jbohac@...e.cz>
Subject: Re: [PATCH 0/2] Make the TSC safe to be used by gettimeofday().

On Mon, 13 Nov 2006, Suleiman Souhlal wrote:

> I believe that the results returned will always be monotonic, as long as the
> frequency of the TSC does not change from under us (that is, without the
> kernel knowing). This is because we "synchronize" each CPU's vxtime with a
> global time source (HPET) every time we know the TSC rate changes.

TSC frequencies of different clocks coming with multiple 
processors may vary which creates a differential even if they are 
initially synchronized.
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