From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751489AbXB0Ec2 (ORCPT ); Mon, 26 Feb 2007 23:32:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751493AbXB0Ec1 (ORCPT ); Mon, 26 Feb 2007 23:32:27 -0500 Received: from mx1.redhat.com ([66.187.233.31]:36642 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751489AbXB0Ec1 (ORCPT ); Mon, 26 Feb 2007 23:32:27 -0500 Message-ID: <45E3B421.603@redhat.com> Date: Mon, 26 Feb 2007 23:31:29 -0500 From: Rik van Riel Organization: Red Hat, Inc User-Agent: Thunderbird 1.5.0.7 (X11/20061008) MIME-Version: 1.0 To: Hiro Yoshioka CC: 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 References: <20070226223645.GA24174@redhat.com> <98df96d30702261632u7479c9b2sce93f80f68bbc8d0@mail.gmail.com> <45E37EA3.3060101@redhat.com> <20070227.130305.424251739.hyoshiok@miraclelinux.com> In-Reply-To: <20070227.130305.424251739.hyoshiok@miraclelinux.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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. Besides, it looks like this is not a problem in MySQL per se (it works on FreeBSD) but some bug in Linux. -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic.