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

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>, "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: Mon, 27 Jul 2009 15:55:08 +0100
Cc: "Dong, Eddie" <eddie.dong@xxxxxxxxx>, John Levon <levon@xxxxxxxxxxxxxxxxx>
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On 27/07/2009 15:47, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> Some googling and reading provides evidence that VMware
> does indeed virtualize the TSC.  The timekeeping paper
> http://www.vmware.com/pdf/vmware_timekeeping.pdf
> tells how to turn vTSC off, but says that turning it
> off is no longer recommended.

I believe this affects the guest OS executing RDTSC, not guest apps, and is
only to delay the TSC to not 'run past' pending timer ticks (typically where
they have been delayed due to the guest being preempted).

 -- Keir



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