From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751455AbXB0IOi (ORCPT ); Tue, 27 Feb 2007 03:14:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751509AbXB0IOi (ORCPT ); Tue, 27 Feb 2007 03:14:38 -0500 Received: from smtp.ono.com ([62.42.230.12]:44824 "EHLO resmaa06.ono.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751455AbXB0IOh (ORCPT ); Tue, 27 Feb 2007 03:14:37 -0500 Date: Tue, 27 Feb 2007 09:14:09 +0100 From: "J.A. =?UTF-8?B?TWFnYWxsw7Nu?=" To: Rik van Riel Cc: Hiro Yoshioka , davej@redhat.com, harlan@artselect.com, nickpiggin@yahoo.com.au, l_allegrucci@yahoo.it, linux-kernel@vger.kernel.org, mingo@elte.hu, suparna@in.ibm.com, jens.axboe@oracle.com Subject: Re: SMP performance degradation with sysbench Message-ID: <20070227091409.6f3d12f9@werewolf-wl> In-Reply-To: <45E3B421.603@redhat.com> References: <20070226223645.GA24174@redhat.com> <98df96d30702261632u7479c9b2sce93f80f68bbc8d0@mail.gmail.com> <45E37EA3.3060101@redhat.com> <20070227.130305.424251739.hyoshiok@miraclelinux.com> <45E3B421.603@redhat.com> X-Mailer: Claws Mail 2.8.0 (GTK+ 2.10.9; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 26 Feb 2007 23:31:29 -0500, Rik van Riel wrote: > Hiro Yoshioka wrote: > > Hi, > > > > From: Rik van Riel > >> 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? > > None. Each schedulable entity (whether a fully fledged > CPU core or an SMT/HT thread) is treated the same. > And what do the SMT and Multi-Core scheduling options in the kernel config are for ? Because of this thread I re-read the help text, and it looks like on could de-select the SMT scheduler option, get a working SMP system, and see what difference ? I suppose its related to migration and cache flushing and so on, but where could I get more details ? And more strange, what is the difference between multi-core and normal SMP configs ? > > 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? > > Not really, that would make it impossible for MySQL to > handle more simultaneous database queries than the system > has CPUs. > I don't know myqsl internals, but you assume one thread per query. If its more like Apache, one long living thread for several connections ? Its the same to answer 4+4 queries than 8 at half the speed, isn't it ? > Besides, it looks like this is not a problem in MySQL > per se (it works on FreeBSD) but some bug in Linux. > -- J.A. Magallon \ Software is like sex: \ It's better when it's free Mandriva Linux release 2007.1 (Cooker) for i586 Linux 2.6.19-jam07 (gcc 4.1.2 20070115 (prerelease) (4.1.2-0.20070115.1mdv2007.1)) #2 SMP PREEMPT