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SubjectRe: (ondemand) CPU governor regression between 2.6.23 and 2.6.24
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It seems to be rather a scheduler issue than a governor issue b/c
the issue went away after unsetting CONFIG_FAIR_GROUP_SCHED.

If I unselect CONFIG_FAIR_GROUP_SCHED then the %CPU value raises 80%
- which forces the ondemand governor do speed up the CPU frequency:


PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
7137 tfoerste 20 0 1796 488 428 R 95.5 0.0 0:01.40 factor
7083 dnetc 39 19 664 348 264 R 2.1 0.0 3:08.33 dnetc
4033 root 20 0 97252 9420 4008 R 0.7 0.9 0:09.43 X


Am Samstag, 26. Januar 2008 schrieben Sie:
> Toralf Förster wrote:
>
> > I use a 1-liner for a simple performance check : "time factor 819734028463158891"
> > Here is the result for the new (Gentoo) kernel 2.6.24:
> >
> > With the ondemand governor of the I get:
> >
> > tfoerste@n22 ~/tmp $ time factor 819734028463158891
> > 819734028463158891: 3 273244676154386297
> >
> > real 0m32.997s
> > user 0m15.732s
> > sys 0m0.014s
> >
> > With the ondemand governor the CPU runs at 600 MHz,
> > whereas with the performance governor I get :
> >
> > tfoerste@n22 ~/tmp $ time factor 819734028463158891
> > 819734028463158891: 3 273244676154386297
> >
> > real 0m10.893s
> > user 0m5.444s
> > sys 0m0.000s
> >
> > (~5.5 sec as I expected) b/c the CPU is set to 1.7 GHz.
> >
> > The ondeman governor of previous kernel versions however automatically increased
> > the CPU speed from 600 MHz to 1.7 GHz.
> >
> > My system is a ThinkPad T41, I'll attach the .config
>
> During the test, run top, and watch your CPU usage. Does it go above 80%
> (the default for
> /sys/devices/system/cpu/cpu0/cpufreq/ondemand/up_threshold).
>
> ondemand CPUfreq governor has a few tunables, described in
> Documentation/cpu-freq. One of them is up_threshold:
>
> up_threshold: defines what the average CPU usaged between the samplings
> of 'sampling_rate' needs to be for the kernel to make a decision on
> whether it should increase the frequency. For example when it is set
> to its default value of '80' it means that between the checking
> intervals the CPU needs to be on average more than 80% in use to then
> decide that the CPU frequency needs to be increased.
>
> What CPUFreq processor driver are you using?
>
>
> I had a similar problem with CPUfreq and dm-crypt (slow reads), see
> (more setup problem than something kernel-related):
>
> http://blog.wpkg.org/2008/01/22/cpufreq-and-dm-crypt-performance-problems/
>
>

--
MfG/Sincerely

Toralf Förster
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