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    SubjectRe: preempt-timing-2.6.8-rc1
    William Lee Irwin III wrote:
    >> Wild guess is that you took an IRQ in dec_preempt_count() and that threw
    >> your results off. Let me know if the patch below helps at all. My guess
    >> is it'll cause more apparent problems than it solves.

    On Tue, Jul 13, 2004 at 06:32:16PM +0300, Lenar L?hmus wrote:
    > Machine in question is XP2500+@1.84GHz (it was overlocked@2.25GHz during
    > last test, now running at
    > official speed). Is this really slow for 1ms?

    It should actually be fast enough. I suspect something else, maybe some
    slow devices. What's /proc/interrupts look like?


    On Tue, Jul 13, 2004 at 06:32:16PM +0300, Lenar L?hmus wrote:
    > Applied your patch. Booted.
    > With preempt_thresh=1 I still got tons of those violations at schedule().
    > With preempt_thresh=2 I do not get those anymore. Apart from sys_ioctl()
    > violation, getting now these:
    > 16ms non-preemptible critical section violated 2 ms preempt threshold
    > starting at exit_notify+0x1d/0x7b0 and ending at schedule+0x291/0x480
    > 7ms non-preemptible critical section violated 2 ms preempt threshold
    > starting at kmap_atomic+0x13/0x70 and ending at kunmap_atomic+0x5/0x20
    > 6ms non-preemptible critical section violated 2 ms preempt threshold
    > starting at fget+0x28/0x70 and ending at fget+0x41/0x70

    exit_notify() isn't a huge surprise unless you're not doing things with
    lots of processes. Actually, it probably is a surprise, since it should
    only hurt when you're doing forkbombs and/or threadbombs.

    The kmap_atomic() stuff is too consistent. Maybe you're taking an
    interrupt during the copy operation.

    fget() is mind-bogglingly O(1) and very short. Only plausible guess is
    we're seeing interrupts taken there because it's so frequently called.


    On Tue, Jul 13, 2004 at 06:32:16PM +0300, Lenar L?hmus wrote:
    > No apparent side-effects noticed.
    > As before, when running mplayer I'm getting many sys_ioctl() things
    > coupled with messages:
    > rtc: lost some interrupts at 1024Hz.
    > It happens when madly seeking around in video.

    Not surprised either. There's probably enough time spent with interrupts
    off the local_irq_save() hurt, and it didn't make your schedule() things
    go away, so my wild guesswork thus far is it made things worse with no
    tangible benefit, so best to drop that local_irq_save() change.


    -- wli
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