Kai Schaetzl wrote:
S.Tindall wrote on Sun, 3 Aug 2008 21:47:06 -0400:
The cpuspeed changelog may be relevant:
[quote]
* Thu Mar 06 2008 Jarod Wilson <jwilson@xxxxxxxxxx>
- Disable freq scaling by default on AMD rev F and earlier cpus
when running xen, due to clock instability (#435321)
[/quote]
Thanks, it didn't occur to me that cpuspeed may also be relevant to this.
However, I don't think it's relevant for the wrong cpu frequency reading
on the 3.2 Xen kernels (which in turn is responsible for the missing
scalability). Cpuspeed is not part of the kernel and did not change during
all my tests. See below for possible explanation.
I didn't look up your cpu, but I think it's a revision F.
Hm, /proc/cpuinfo doesn't show any revision number. A bit googling tells
me that the CPUs, at least the second one, are more likely to be rev. H or
above. The older one is a 3800+ EE and the newer one is a 4850e which I
bought right after it became available. Unless rev. G and up are only quad
core CPUs at least the latter 45nm one should be rev G or up, too. But I
can't find a definitive list, shouldn't there be one on the AMD site?
Maybe this is relevant to you:
http://www.centos.org/modules/newbb/viewtopic.php?topic_id=15328&forum=41
quote
# Frequency scaling on AMD rev F CPUs under Xen can result in
# timekeeping problems for fully virtualized guests, so we disable
# it by default.
if [ -d /proc/xen ] && [ "$cpu_vendor" == AuthenticAMD ] \
&& [ "$cpu_family" -le 15 ]; then
default_governor=performance
fi
/quote
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