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Date: Fri, 07 Feb 2003 17:57:46 -0800
From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Andi Kleen <ak@suse.de>, john stultz <johnstul@us.ibm.com>
cc: lkml <linux-kernel@vger.kernel.org>, Joel Becker <Joel.Becker@oracle.com>
Subject: Re: [RFC][PATCH] linux-2.5.59_getcycles_A0
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>> However this doesn't work on systems w/o a synced TSC, so by simply
> 
> Why not? This shouldn't be performance critical and you can make 
> it monotonous with an additional variable + lock if backwards jumps
> should be a problem.
> 
> Also the variations between non synced TSCs should be far below 
> any watchdog's radar screen.

Not true. They'll drift further and further apart over time.
Even a 0.01% crystal difference will eventually kill you.

And if that isn't bad enough think about what happens when I run 180 MHz
processors in one node, and 900MHz in another.

You really can't make any assumptions about TSC sync on boxes where
they're not synced.

M.