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RE: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron 2nd gen

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Ralf Schenk" <rs@xxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron 2nd gen and earlier processors
From: "Langsdorf, Mark" <mark.langsdorf@xxxxxxx>
Date: Tue, 29 Jan 2008 10:13:38 -0600
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thread-topic: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron 2nd gen and earlier processors
> > Actually I've now eyeballed the problem. We access a stack 
> > variable after the stack frame is gone away. Probably we
> > therefore end up setting a CPU's frequency to zero, which
> > is not good at all. I'll work up a fix.
> 
> Changeset 16927 should fix the problem for you.

16927 seems to have resolved the problem.  I'll be running
a stress test in the background all day, but the prelimary
results show that:

a) the machine isn't locking up on boot any more
b) pstate transitions are possible without having the time
        go backwards on a regular basis

Ian was right about the design of Xen's time-keeping.

-Mark Langsdorf
Operating System Research Center
AMD

PS - Ralk, could you please test this on your machine?



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