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Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy lo

From: David S. Ahern
Subject: Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load.
Date: Thu, 06 Nov 2008 10:28:44 -0700
User-agent: Thunderbird (X11/20080723)

Dor Laor wrote:
> Gleb Natapov wrote:
>> On Fri, Oct 31, 2008 at 02:17:19PM -0500, Anthony Liguori wrote:
>>> Gleb Natapov wrote:
>>>> Qemu device emulation for timers might be inaccurate and
>>>> causes coalescing of several IRQs into one. It happens when the
>>>> load on the host is high and the guest did not manage to ack the
>>>> previous IRQ. The problem can be reproduced by copying of a big
>>>> file or many small ones inside Windows guest. When you do that guest 
>>>> clock start to lag behind the host one.


>>>                                                                 How do  
>>> Linux guests behave with this?
>> Linux guests don't use pit or RTC for time keeping. They are completely
>> unaffected by those patches.
> It will probably also drift with clock=pit in the guest kernel cmdline.

It is my understanding that for linux guests using a 2.4 kernel (e.g.,
RHEL3) the PIT is the only option.


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