Re: cpufreq on VIA C7

> Date: Sun, 02 Aug 2009 13:35:28 +0200
> From: Harald Schmalzbauer <h.schmalzbauer_at_omnilan.de>
> Sender: owner-freebsd-current_at_freebsd.org
> 
> Uwe Grohnwaldt schrieb am 01.08.2009 01:49 (localtime):
> > Hi,
> > 
> > disabling cpufreq in the kernel configfile works fine. after that it 
> > looks fine:
> > dev.cpu.0.freq_levels: 2000/20000 1000/10000 800/8000 400/4000
> 
> This is done by throttling. Unfortunately it doesn't safe power for me, 
> at least on my E8400 the power consumption raises about a hardly 
> measureable bit.
> If I'm right the C7 (Eden V4, Esther in my case) supports enhanced speed 
> stepping. I can enable it in my BIOS (along with SpeedStep1) which 
> should enable the cpu to operate with 0.884 Volt. This would safe 
> enourmous power.
> Unfortunately I can't hack the est driver to attach to C7.
> Any volunteers? :)
> 
> Best regards,
> 
> -Harry
> 
> P.S.: I'll do some measurings regarding the throttling on the C7 to 
> verify disabling throttling is the right thing ;)

As I post fairly often, throttling seldom helps power consumption on ANY
processor. All throttling (and TCC) do is to skip N of every 8 clock
cycles. That means performance is cut exactly the same as
power. Running any given job takes almost exactly the same amount of
power, just taking longer as the throttling is increased.

>From my limited reading of Intel docs, the primitive throttling and more
advanced TCC were introduced for thermal management, where they actually
do work and not power management, where they don't. TCC is the TLA for
Thermal Control Circuit.

I have seen it suggested that throttling should be removed from power
management and I heartily endorse this. I always disable it (along with
TCC). 
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman_at_es.net			Phone: +1 510 486-8634
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