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    SubjectRe: Update on Timer Frequencies
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    On Wed, 2005-11-09 at 23:35 -0500, Steven Rostedt wrote:
    > On Mon, 2005-11-07 at 22:58 -0500, Steven Rostedt wrote:
    > >
    >
    > Running my logdev tools from:
    > http://www.kihontech.com/logdev/logdev_tools_0.3.0.tar.bz2
    >
    > ./logread /dev/logdev > 1000HZ.out # with 1000HZ
    > ./logread /dev/logdev > 100HZ.out # with 100HZ
    >
    > These files can be found at:
    > http://www.kihontech.com/tests/hz_times/
    >
    > These show all the times that a context switch took place. This is a
    > ring buffer, so it only captured the last 30 some seconds of the test.
    > But that should be good enough.
    >
    > with my analyze.pl script (also supplied at the website) I ran:
    >
    > ./analyze.pl 1000HZ.out > 1000HZ.txt
    > and again for 100HZ.
    >
    > This calculates the times between the context switches and at the end
    > produces an average.
    >
    > (all times are in seconds)
    >
    > For 100HZ:
    >
    > [54543.530810] CPU:0 (testme:2539) -->> (find:2550)
    > diff: 0.000213
    > [54543.546730] CPU:0 (find:2550) -->> (testme:2539)
    > diff: 0.015920
    > count: 28974 total: 38.384180
    > average: 0.001325

    The above 100HZ test is invalid. As shown in the times, it was run
    after 54000 some seconds, which means that the file system was probably
    already cached. So I did fresh reboots and ran the test shortly after
    bootup.

    The test results are again at http://www.kihontech.com/tests/hz_times/
    but they are all with a *_2.* in the name.

    Here are the times that were run for each test (100HZ vs 1000HZ and
    preempt vs nopreempt).

    1000HZ preempt:
    Thu Nov 10 18:05:11 EST 2005
    Thu Nov 10 18:13:01 EST 2005

    real 7m49.741s
    user 0m46.464s
    sys 4m41.524s


    1000HZ nopreempt:
    Thu Nov 10 22:17:33 EST 2005
    Thu Nov 10 22:25:15 EST 2005

    real 7m42.339s
    user 0m47.156s
    sys 4m33.205s


    100HZ preempt:
    # time ./testme
    Thu Nov 10 17:40:29 EST 2005
    Thu Nov 10 17:48:12 EST 2005

    real 7m42.418s
    user 0m46.190s
    sys 4m40.350s


    100HZ nopreempt:
    Thu Nov 10 17:52:15 EST 2005
    Thu Nov 10 17:59:56 EST 2005

    real 7m40.976s
    user 0m44.840s
    sys 4m34.510s

    This seems to show that 100HZ with no preemption was the fastest, but
    the times are too close, so it is of a difference of ~0.2% which is well
    in the margin of error. So this test really doesn't show much benefit
    between the settings.

    Tomorrow, I'll see if I can make a test that serves up web pages, and
    see if that will show the benefits for servers and the settings for HZ
    and preemption.

    -- Steve


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