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Re: [Xen-devel] write_tsc in a PV domain?

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] write_tsc in a PV domain?
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 31 Aug 2009 20:06:02 +0100
Cc: "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
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On 31/08/2009 19:11, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> I have yet to get a measurement of either syscall that
> is better than 2.5x WORSE than emulating rdtsc. On
> my dual-core Conroe (Intel E6850) with 64-bit Xen and
> 32-bit dom0, I get approximately:
> rdtsc native: 22ns
> softtsc (rdtsc emulated): 360ns

Trap-and-emulate in 360ns seems astoundingly good. Perhaps too good to be

 -- Keir

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