linux-kernel - Re: cpuinfo shows wrong MHz value

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Date:	Wed, 18 Feb 2009 20:54:38 +0100
From:	Joerg Platte <jplatte@...sa.net>
To:	Frans Pop <elendil@...net.nl>
Cc:	Kasper Sandberg <lkml@...anurb.dk>, linux-kernel@...r.kernel.org
Subject: Re: cpuinfo shows wrong MHz value

Am Sonntag, 15. Februar 2009 schrieben Sie:
> Can you check whether or not you were also using p4-clockmode with the
> last kernel that did show correct values? The same grep command should
> show this.

The last kernel that was working correct was 2.6.24 (here the output from 
2.6.24.6):

affected_cpus:0
cpuinfo_cur_freq:1600000
cpuinfo_max_freq:1600000
cpuinfo_min_freq:400000
scaling_available_frequencies:400000 600000 800000 1000000 1200000 1400000 
1600000
scaling_available_governors:conservative ondemand userspace powersave 
performance
scaling_cur_freq:1600000
scaling_driver:p4-clockmod
scaling_governor:performance
scaling_max_freq:1600000
scaling_min_freq:400000
root@...o:/sys/devices/system/cpu/cpu0/cpufreq> uname -a
Linux jako 2.6.24.6 #1 PREEMPT Tue Feb 17 20:33:58 CET 2009 i686 GNU/Linux

The log output is somewhat limited, because I forgot to enable debugging:

root@...o:/sys> dmesg | grep clock
Time: tsc clocksource has been installed.
intel8x0_measure_ac97_clock: measured 55906 usecs
intel8x0: measured clock 71 rejected
intel8x0: clocking to 48000
p4-clockmod: P4/Xeon(TM) CPU On-Demand Clock Modulation available

Here is the output from 2.6.28.5 and debug info enabled:
root@...o:~> dmesg | grep clock
intel8x0_measure_ac97_clock: measured 55894 usecs
intel8x0: measured clock 71 rejected
intel8x0: clocking to 48000
p4-clockmod: P4/Xeon(TM) CPU On-Demand Clock Modulation available

It looks like the debug code does not provide more information.

> It would also help to know which kernel version was the last working one.
> You mentioned 2.6.26, but with some uncertainty. Can you check for 2.6.26
> and possibly for 2.6.27?

I was wrong, it was working long ago with kernel 2.6.24, sorry. 

> Note that p4-clockmode does not really help with power saving, but only
> with thermal management (prevention of overheating). Possibly the
> speedstep or acpi-cpufreq modules will work better for you, but it can
> also be they don't support your processor.

Yes, I know. I just installed it to play with it and now I'm using the 
performance governor all the time which disables frequency modulation.

> That does not mean this issue should not be looked into of course.

I can simply unload the module but a fix would be appreciated as well :)

regards,
Jörg
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