linux-kernel - Re: [kvm-devel] Guest kernel hangs in smp kvm for older kernels prior to tsc sync cleanup

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Message-ID: <47693B9D.7080809@qumranet.com>
Date:	Wed, 19 Dec 2007 17:41:17 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Glauber de Oliveira Costa <glommer@...il.com>
CC:	Avi Kivity <avi@...o.co.il>, Ingo Molnar <mingo@...e.hu>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Gerd Hoffmann <kraxel@...hat.com>
Subject: Re: [kvm-devel] Guest kernel hangs in smp kvm for older kernels prior
 to tsc sync cleanup

Glauber de Oliveira Costa wrote:
> Changes in rate does not sound good. It's possibly what's screwing up
> my paravirt clock implementation in smp.
>   

You should renew the timebase on vcpu migration, and hook cpufreq so 
that changes in frequency are reflected in the timebase.

> Since the host updates guest time prior to putting vcpu to run, two
> vcpus that start running at different times will have different system
> values.
>
> Now if the vcpu that started running later probes the time first,
> we'll se the time going backwards. A constant tsc rate is the only way
> around
> my limited mind sees around the problem (besides, obviously, _not_
> making the system time per-vcpu).
>   

I tried disabling frequency scaling (rmmod acpi_cpufreq) but that didn't 
help my present problems.

-- 
error compiling committee.c: too many arguments to function

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