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    SubjectRe: SMP performance degradation with sysbench
    Nick Piggin wrote:
    > Rik van Riel wrote:
    >
    >> Lorenzo Allegrucci wrote:
    >>
    >>> Hi lkml,
    >>>
    >>> according to the test below (sysbench) Linux seems to have scalability
    >>> problems beyond 8 client threads:
    >>> http://jeffr-tech.livejournal.com/6268.html#cutid1
    >>> http://jeffr-tech.livejournal.com/5705.html
    >>> Hardware is an 8-core amd64 system and jeffr seems willing to try more
    >>> Linux versions on that machine.
    >>> Anyway, is there anyone who can reproduce this?
    >>
    >>
    >>
    >> I have reproduced it on a quad core test system.
    >>
    >> With 4 threads (on 4 cores) I get a high throughput, with
    >> approximately 58% user time and 42% system time.
    >>
    >> With 8 threads (on 4 cores) I get way lower throughput,
    >> with 37% user time, 29% system time 35% idle time!
    >>
    >> The maximum time taken per query also increases from
    >> 0.0096s to 0.5273s. Ouch!
    >>
    >> I don't know if this is MySQL, glibc or Linux kernel,
    >> but something strange is going on...
    >
    >
    > Like you, I'm also seeing idle time start going up as threads increase.
    >
    > I initially thought this was a problem with the multiprocessor scheduler,
    > because the pattern is exactly like some artificat in the load balancing.

    "artificat"

    Wow. I must need some sleep :) Please excuse any other typos!

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