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    SubjectRe: BFS vs. mainline scheduler benchmarks and measurements
    On 09/08/2009 05:20 PM, Arjan van de Ven wrote:
    > On Tue, 08 Sep 2009 13:13:34 +0300
    > Nikos Chantziaras<realnc@arcor.de> wrote:
    >
    >> On 09/08/2009 11:38 AM, Arjan van de Ven wrote:
    >>> On Tue, 08 Sep 2009 10:19:06 +0300
    >>> Nikos Chantziaras<realnc@arcor.de> wrote:
    >>>
    >>>> latencytop has this to say:
    >>>>
    >>>> http://foss.math.aegean.gr/~realnc/pics/latop1.png
    >>>>
    >>>> Though I don't really understand what this tool is trying to tell
    >>>> me, I hope someone does.
    >>>
    >>> despite the untranslated content, it is clear that you have
    >>> scheduler delays (either due to scheduler bugs or cpu contention)
    >>> of upto 68 msecs... Second in line is your binary AMD graphics
    >>> driver that is chewing up 14% of your total latency...
    >>
    >> I've now used a correctly installed and up-to-date version of
    >> latencytop and repeated the test. Also, I got rid of AMD's binary
    >> blob and used kernel DRM drivers for my graphics card to throw fglrx
    >> out of the equation (which btw didn't help; the exact same problems
    >> occur).
    >>
    >> Here the result:
    >>
    >> http://foss.math.aegean.gr/~realnc/pics/latop2.png
    >>
    >> Again: this is on an Intel Core 2 Duo CPU.
    >
    >
    > so we finally have objective numbers!
    >
    > now the interesting part is also WHERE the latency hits. Because
    > fundamentally, if you oversubscribe the CPU, you WILL get scheduling
    > latency.. simply you have more to run than there is CPU.

    Sounds plausible. However, with mainline this latency is very, very
    noticeable. With BFS I need to look really hard to detect it or do
    outright silly things, like a "make -j50". (At first I wrote "-j20"
    here but then went ahead an tested it just for kicks, and BFS would
    still let me use the GUI smoothly, LOL. So then I corrected it to
    "-j50"...)


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