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Date: Tue, 18 Oct 2016 19:05:14 -0200
From: Eduardo Habkost <ehabkost@redhat.com>
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Subject: Re: [Qemu-devel] invtsc + migration + TSC scaling
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To: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org

On Tue, Oct 18, 2016 at 10:52:14PM +0200, Radim Kr=C4=8Dm=C3=A1=C5=99 wro=
te:
[...]
> The main problem is that QEMU changes virtual_tsc_khz when migrating
> without hardware scaling, so KVM is forced to get nanoseconds wrong ...
>=20
> 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
CPUID?

--=20
Eduardo