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    SubjectRe: Linus 2.6.23-rc1

    On Jul 28 2007 12:34, Linus Torvalds wrote:
    >On Sat, 28 Jul 2007, Jan Engelhardt wrote:
    >>
    >> Time to investigate...

    Well it really is different.

    Simple test:
    - run Unreal Tournament 99 (nice 0, it gets 98%,99% CPU most of the time)
    - in a shell, `renice 20 $$; while :; do date; done;`

    The shell only produces one or two outputs per second.
    This seems different from the old-2.6 behavior, where a nice-20
    process seemed to get a bit more share. (Due to interactivity bonus)


    Does anyone have a cpu hog test program that spreads its cpu time
    over the second rather than doing 300 ms wake and 700 ms sleep cycles
    after another?

    >Well, one thing that would be worth doing is to simply create a trace of
    >time-slices for both schedulers.
    >
    >It could easily be some hacky thing that just saves the process name and
    >TSC at each scheduling event in some fairly small fixed-sized per-CPU
    >circular buffer, and have a /sys interface that reads it out, and then you
    >do
    >
    > sleep 60 ; cat /sys/cpubuffer > buffer
    >
    >and play the game for 60 seconds (so that you get a buffer that represents
    >perhaps the last 10 seconds of play).

    Send me patches, I run the test.

    >It could *literally* just be an effect of the time quanta used, and CFS
    >just deciding that it's not interactive and giving things too long of a
    >CPU slice.
    >
    >Yes, it's what "/proc/sys/kernel/sched_granularity_ns" is supposed to
    >tweak, but maybe there's some misfeature there, or maybe the default is
    >just bad for games, or whatever.
    >
    >Ingo: that sysctl_sched_granularity initialization doesn't make sense. You
    >talk about it being in units of nanoseconds, but then you do
    >
    > 2000000000ULL/HZ
    >
    >which is nonsensical. That value is "2 seconds" (not 2ms like the comment
    >says) in nanoseconds, but then divided by HZ, so what's the meaning of
    >that HZ thing? Nothing in the scheduler should care about jiffies, why is
    >that related to HZ? All the scheduler clocks are in ns.
    >
    > Linus
    >

    Jan
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