linux-kernel - Re: SMP performance degradation with sysbench

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Date:	Tue, 27 Feb 2007 18:20:25 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	hyoshiok@...aclelinux.com
Cc:	Dave Jones <davej@...hat.com>, Pete Harlan <harlan@...select.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Rik van Riel <riel@...hat.com>,
	Lorenzo Allegrucci <l_allegrucci@...oo.it>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: SMP performance degradation with sysbench

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
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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