linux-kernel - Re: SMP performance degradation with sysbench

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Message-Id: <20070227.130305.424251739.hyoshiok@miraclelinux.com>
Date:	Tue, 27 Feb 2007 13:03:05 +0900 (JST)
From:	Hiro Yoshioka <hyoshiok@...aclelinux.com>
To:	riel@...hat.com
Cc:	davej@...hat.com, harlan@...select.com, nickpiggin@...oo.com.au,
	l_allegrucci@...oo.it, linux-kernel@...r.kernel.org, mingo@...e.hu,
	suparna@...ibm.com, jens.axboe@...cle.com,
	hyoshiok@...aclelinux.com
Subject: Re: SMP performance degradation with sysbench

Hi,

From: Rik van Riel <riel@...hat.com>
> 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)
snip
> > MySQL tries to get a mutex but it spends about 16.8% of CPU on 8 core
> > machine.
> > 
> > I think there are a lot of room to be inproved in MySQL implementation.
> 
> That's one aspect.
> 
> The other aspect of the problem is that when the number of
> threads exceeds the number of CPU cores, Linux no longer
> manages to keep the CPUs busy and we get a lot of idle time.
> 
> On the other hand, with the number of threads being equal to
> the number of CPU cores, we are 100% CPU bound...

I have a question. If so, what is the difference of kernel's
view between SMP and CPU cores?

Another question. When the number of threads exceeds the number of
CPU cores, we may get a lot of idle time. Then a workaround of
MySQL is that do not creat threads which exceeds the number
of CPU cores. Is it right?

Regards,
  Hiro
--
Hiro Yoshioka
CTO/Miracle Linux Corporation
http://blog.miraclelinux.com/yume/
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