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[Xen-devel] Re: TSC scaling and softtsc reprise, and PROPOSAL

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: TSC scaling and softtsc reprise, and PROPOSAL
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 28 Jul 2009 16:00:14 +0100
Cc: "Dong, Eddie" <eddie.dong@xxxxxxxxx>, John Levon <levon@xxxxxxxxxxxxxxxxx>
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On 28/07/2009 15:45, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> I am proposing that the virtual TSC be the default.
> We should provide a per-VM option and a Xen boot
> option to allow VMs to NOT trap rdtsc, but this
> should have a warning that it is not recommended
> and may result in data corruption in some apps.

This I can agree with. The softtsc boot option is just lazy. This should
properly be a per-VM option, for both HVM and PV guests. For example
tsc_freq=x sets virtual TSC of x MHz. And not specifying tsc_freq gets you
current behaviour (pass through host TSC where possible). That I could quite
happily live with, although I'm not planning to implement it myself.

 -- Keir

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