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

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Message-ID: <4D25A710.5030500@redhat.com>
Date:	Thu, 06 Jan 2011 01:27:12 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Alexander Graf <agraf@...e.de>
CC:	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [KVM TSC trapping / migration 2/2] Add TSC KHZ MSR

On 01/06/2011 12:34 AM, Alexander Graf wrote:
> 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.
>
>    

Unfortunately, no.
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