Re: SMP performance degradation with sysbench

[Eric Dumazet]

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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