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Date: Tue, 25 Mar 2003 18:28:37 -0800
From: george anzinger <george@mvista.com>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: Fionn Behrens <fionn@unix-ag.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: System time warping around real time problem - please help
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Alan Cox wrote:
> On Tue, 2003-03-25 at 22:55, Fionn Behrens wrote:
> 
>>>This all sounds very much like the TSCs are drifting WRT each other. 
>>>Is it possible that you have some power management code (or hardware) 
>>>that is slowing one cpu and not the other?
>>
>>Well, I still don't really know what TSCs actually are (or what TSC
>>stands for).

Stands for Time Stamp Counter.  It is a special cpu register that 
basically counts cpu cycles.  Some times (incorrectly me thinks) it is 
affected by power management code which slows the cpu by changing the 
cpu frequency.
>>
>>The only suspect in that case would be the amd76x_pm.o kernel module
>>which I am admittedly using. It saves about 90Watts of power when the
>>machine is idle...
> 
> 
> If you are using amd76x_pm boot with "notsc", ditto for that matter
> on dual athlons with APM or ACPI in some cases. In fact I wish people
> would stop using the tsc for clock timing altogether. It simply doesn't
> work on a lot of modern systems
> 
I agree, however, what is really needed is not available in x86 
machines, i.e. a cpu register that has a fixed and stable count rate. 
  An I/O register is second best because of the long time it takes to 
read it.
> 
> 

-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml

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