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Re: [Qemu-devel] invtsc + migration + TSC scaling

From: Eduardo Habkost
Subject: Re: [Qemu-devel] invtsc + migration + TSC scaling
Date: Tue, 18 Oct 2016 19:05:14 -0200
User-agent: Mutt/1.7.0 (2016-08-17)

On Tue, Oct 18, 2016 at 10:52:14PM +0200, Radim Krčmář wrote:
> The main problem is that QEMU changes virtual_tsc_khz when migrating
> without hardware scaling, so KVM is forced to get nanoseconds wrong ...
> If QEMU doesn't want to keep the TSC frequency constant, then it would
> be better if it didn't expose TSC in CPUID -- guest would just use
> kvmclock without being tempted by direct TSC accesses.

Isn't enough to simply not expose invtsc? Aren't guests expected
to assume the TSC frequency can change if invtsc isn't set on


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