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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
    pgp finger print: 7B1A 07F4 EC82 0F90 D4C2 8936 872A E508 7DB6 9DA3
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