FC4 Kernel 2.6.14-1.1656_FC4smp shows wrong clock rate on Opteron 875

[James Wilkinson]

Joachim Backes [RHRK] wrote:
> I'm running a Sun Fire V40Z server with 4xAMD Opteron 875 dual core 
> (2.2Ghz). But looking for /proc/cpuinfo
> shows for example for each (of eight) processors:
<snip>
> I'm wondering about the clock 997 Mhz, because each processor should run 
> with 2.2 Ghz.
> Is this a display problem only, or does each processor core really run 
> with 0.9 Ghz rate?

This is almost certainly due to cpuspeed. AMD64 processors come with
what AMD call "Cool'n'Quiet", and Fedora knows how to use this. On a
single-processor system, the processor will be slowed down to ~ 1 GHz
(or 800 MHz on older processors) when there isn't much work for
the processor to do. The voltage will be lowered, too, which saves quite
a bit of power. That means there's heat being given off, which means the
fans can go slower or stop, which means even less power.

When system load picks up, the processor is returned to its "normal"
operating speed.

I don't have experience with multi-CPU Opteron machines under Linux, but
I strongly suspect the same thing applies.

Hope this helps,

James.

-- 
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