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[Xen-devel] Re: Linux questions

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: [Xen-devel] Re: Linux questions
From: Andi Kleen <andi@xxxxxxxxxxxxxx>
Date: Tue, 04 Dec 2007 12:13:41 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Jan Beulich <jbeulich@xxxxxxxxxx>, Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>
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In-reply-to: <C37AE293.195B6%Keir.Fraser@xxxxxxxxxxxx> (Keir Fraser's message of "Tue\, 04 Dec 2007 10\:55\:15 +0000")
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Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> writes:

> On 4/12/07 10:23, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
>> I have to disagree: At least the uses of barrier() in monotonic_clock() 
>> appear
>> to be in places where in reality (and from a theoretical standpoint) rmb()
>> ought to be used.
>
> We're sync'ing against concurrent updates of a this_cpu variable. We can
> only race updates in a local ISR, and hence barrier() suffices.

Not if you use RDTSC inside the loop.

-Andi

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