linux-kernel - Re: [KVM TSC trapping / migration 2/2] Add TSC KHZ MSR

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Date:	Thu, 6 Jan 2011 11:34:43 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Zachary Amsden <zamsden@...hat.com>
Cc:	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Zachary Amsden <zamsden@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [KVM TSC trapping / migration 2/2] Add TSC KHZ MSR


Am 06.01.2011 um 11:10 schrieb Zachary Amsden <zamsden@...hat.com>:

> Use an MSR to allow "soft" migration to hosts which do not support
> TSC trapping.  Rather than make this a required element of any
> migration protocol, we allow the TSC rate to be exported as a data
> field (useful in its own right), but we also allow a one time write
> of the MSR during VM creation.  The result is that for the common
> use case, no protocol change is required to communicate TSC rate
> to the receiving host.
> 
> This allows administrative tools to configure migration policy
> as they see appropriate.  Rather than dictate this policy with the
> KVM implementation, we properly allow migration to hosts which both
> do and do not support setting of the TSC rate on the receiving end.
> If it is wished to not support migration to a host which lacks
> support for the TSC rate feature, that can be coordinated externally.

Isn't there a real hw equivalent of such a register? It might make more sense to just implement that then.


Alex

> 
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