Re: SMP performance degradation with sysbench

Hiro Yoshioka
2007-02-28T01:30:28Z

From: Robert Hancock <hancockr@shaw.ca>
Subject: Re: SMP performance degradation with sysbench
Date: Tue, 27 Feb 2007 18:20:25 -0600
Message-ID: <45E4CAC9.4070504@shaw.ca>

> 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?

Yes, it is.

Regards,
Hiro