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

To: "Langsdorf, Mark" <mark.langsdorf@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Disable Xen PowerNow! support on Opteron 2nd gen and earlier processors
From: Ralf Schenk <rs@xxxxxxxxxx>
Date: Mon, 11 Feb 2008 12:27:05 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
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Langsdorf, Mark schrieb:
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

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


thanks for your discussion and efforts to solve the Problems.

For your information: I'm running ondemand scheduler in Dom0 now with

(XEN) Xen version 3.2.1-rc1-pre (root@xxxxxxxxxxxxxxxxx) (gcc version 4.0.3 (Ubuntu 4.0.3-1ubuntu5)) Sat Feb 9 13:07:11 CET 2008
(XEN) Latest ChangeSet: Wed Feb 06 10:06:35 2008 +0000 16759:d26b1b777fde

since Saturday and I haven't had "Time went backwards" messages in my DomU's so far. Switching is working depending on the CPU Load in Domu as expected. But mostly the system stays at 1Ghz.

From cpuinfo:
processor       : 1
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 107
model name      : AMD Athlon(tm) 64 X2 Dual Core Processor 5000+
stepping        : 2
cpu MHz         : 1000.000
cache size      : 512 KB


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