Re: SMP performance degradation with sysbench

Robert Hancock
2007-02-28T00:24:31Z

Hiro Yoshioka wrote:
> Howdy,
>
> MySQL 5.0.26 had some scalability issues and it solved since 5.0.32
> http://ossipedia.ipa.go.jp/capacity/EV0612260303/
> (written in Japanese but you may read the graph. We compared
> 5.0.24 vs 5.0.32)
>
> The following is oprofile data
> ==>
> cpu=8-mysql=5.0.32-gcc=3.4/oprofile-eu=2200-op=default-none/opreport-l.txt
> <==
> CPU: Core Solo / Duo, speed 2666.76 MHz (estimated)
> Counted CPU_CLK_UNHALTED events (Unhalted clock cycles) with a unit
> mask of 0x00 (Unhalted core cycles) count 100000
> samples % app name symbol name
> 47097502 16.8391 libpthread-2.3.4.so pthread_mutex_trylock
> 19636300 7.0207 libpthread-2.3.4.so pthread_mutex_unlock
> 18600010 6.6502 mysqld rec_get_offsets_func
> 18121328 6.4790 mysqld btr_search_guess_on_hash
> 11453095 4.0949 mysqld row_search_for_mysql
>
> MySQL tries to get a mutex but it spends about 16.8% of CPU on 8 core
> machine.

Curious that it calls pthread_mutex_trylock (as opposed to
pthread_mutex_lock) so often. Maybe they're doing some kind of mutex
lock busy-looping?

--
Robert Hancock Saskatoon, SK, Canada
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