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    SubjectRe: SMP performance degradation with sysbench
    Anton Blanchard a écrit :
    >
    > Hi Nick,
    >
    >> Anyway, I'll keep experimenting. If anyone from MySQL wants to help look
    >> at this, send me a mail (eg. especially with the sched_setscheduler issue,
    >> you might be able to do something better).
    >
    > I took a look at this today and figured Id document it:
    >
    > http://ozlabs.org/~anton/linux/sysbench/
    >
    > Bottom line: it looks like issues in the glibc malloc library, replacing
    > it with the google malloc library fixes the negative scaling:
    >
    > # apt-get install libgoogle-perftools0
    > # LD_PRELOAD=/usr/lib/libtcmalloc.so /usr/sbin/mysqld

    Hi Anton, thanks for the report.
    glibc has certainly many scalability problems.

    One of the known problem is its (ab)use of mmap() to allocate one (yes : one
    !) page every time you fopen() a file. And then a munmap() at fclose() time.


    mmap()/munmap() should be avoided as hell in multithreaded programs.
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