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    SubjectRe: CFS review
    Date
    Linus Torvalds wrote:
    > On Tue, 28 Aug 2007, Al Boldi wrote:
    > > No need for framebuffer. All you need is X using the X.org vesa-driver.
    > > Then start gears like this:
    > >
    > > # gears & gears & gears &
    > >
    > > Then lay them out side by side to see the periodic stallings for ~10sec.
    >
    > I don't think this is a good test.
    >
    > Why?
    >
    > If you're not using direct rendering, what you have is the X server doing
    > all the rendering, which in turn means that what you are testing is quite
    > possibly not so much about the *kernel* scheduling, but about *X-server*
    > scheduling!
    >
    > I'm sure the kernel scheduler has an impact, but what's more likely to be
    > going on is that you're seeing effects that are indirect, and not
    > necessarily at all even "good".
    >
    > For example, if the X server is the scheduling point, it's entirely
    > possible that it ends up showing effects that are more due to the queueing
    > of the X command stream than due to the scheduler - and that those
    > stalls are simply due to *that*.
    >
    > One thing to try is to run the X connection in synchronous mode, which
    > minimizes queueing issues. I don't know if gears has a flag to turn on
    > synchronous X messaging, though. Many X programs take the "[+-]sync" flag
    > to turn on synchronous mode, iirc.

    I like your analysis, but how do you explain that these stalls vanish when
    __update_curr is disabled?


    Thanks!

    --
    Al

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