[CentOS] Questions on cpu frequency scaling AMD vs. Intel

Mon Aug 4 12:31:16 UTC 2008
Kai Schaetzl <maillists at conactive.com>

Ned Slider wrote on Mon, 04 Aug 2008 10:34:57 +0100:

> 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

That's the patch mentioned by Steve. I didn't look in the cpuspeed init 
file earlier, I did now - it's inside it. As I assumed it doesn't load 
ondemand. Both my cpus are "family 15", so this applies. However, I'm not 
running fully virtualized guests. Nevertheless, the time warning occurs, 
not only in domU, but also in dom0. However, I think it's harmless. Time 
is absolutely stable in dom0 and domU. Maybe that may be change under more 
load. Maybe it's less harmless in fully virtualized machines.

It's a pity that so few information is available.


Kai Schätzl, Berlin, Germany
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