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Re: [Xen-devel] RE: rdtsc: correctness vs performance on Xen (and KVM?)

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] RE: rdtsc: correctness vs performance on Xen (and KVM?)
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: 2009年9月02日 08:20:06 +0100
Cc: "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Delivery-date: 2009年9月02日 00:22:34 -0700
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Thread-topic: [Xen-devel] RE: rdtsc: correctness vs performance on Xen (and KVM?)
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On 02/09/2009 00:26, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:
> On 09/01/09 15:41, Dan Magenheimer wrote:
>> Won't pvclock+vsyscall have the same race?
>
> Yes, it would need to be resolved either way.
The problem is a bit easier with vsyscall potentially. For example, give
each thread its own vsyscall clock data area (easy?), updated by kernel
whenever the thread is scheduled, and increment a version counter, checked
before and after by the vsyscall operation.
Well, I don't know how easy or fast that could actually be implemented, but
I'm at least confident it could work. But it does need kernel assistance.
 -- Keir
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