From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751157AbXB1CXu (ORCPT ); Tue, 27 Feb 2007 21:23:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751161AbXB1CXu (ORCPT ); Tue, 27 Feb 2007 21:23:50 -0500 Received: from smtp102.plus.mail.mud.yahoo.com ([68.142.206.235]:24872 "HELO smtp102.plus.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751157AbXB1CXt (ORCPT ); Tue, 27 Feb 2007 21:23:49 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=0aVU3H+wib36f7h16JpIabq0o4VmLV0Y0U+0HFNGlfpzQmzis1N5cgIQZ1AplkkqEAnQCmfIDBB6se1mgyy1/4HagCFszwAy9hv+VaJNjSSJeyJOMabezgmZDzaW6DKrY8Q+B+g7AgfWW2doE4TxG+lNJ1SfZgl09bImNt8cNBU= ; X-YMail-OSG: IU84U5cVM1lZyOBXjVeraLfHnsKBBxUzmmZfelVD3096Ms3z0h73zcDa.r9WMt3MTuwGBxG.0W3rU7CTZaPd8GWSmQCvY0JNjyvUIlWYNRuCkLrWqfHV50V.a8Rjbnpax6WNXEZnGzL7LZY- Message-ID: <45E4E780.8010109@yahoo.com.au> Date: Wed, 28 Feb 2007 13:22:56 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Nish Aravamudan CC: Rik van Riel , Lorenzo Allegrucci , linux-kernel@vger.kernel.org, Ingo Molnar , Suparna Bhattacharya , Jens Axboe Subject: Re: SMP performance degradation with sysbench References: <1172425476.5489.11.camel@odyssey.lan> <45E21FEC.9060605@redhat.com> <45E2E244.8040009@yahoo.com.au> <29495f1d0702271727w358cc9o644c4017d50634a9@mail.gmail.com> In-Reply-To: <29495f1d0702271727w358cc9o644c4017d50634a9@mail.gmail.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Nish Aravamudan wrote: > On 2/26/07, Nick Piggin wrote: > >> Rik van Riel wrote: >> > Lorenzo Allegrucci wrote: >> > >> >> Hi lkml, >> >> >> >> according to the test below (sysbench) Linux seems to have scalability >> >> problems beyond 8 client threads: >> >> http://jeffr-tech.livejournal.com/6268.html#cutid1 >> >> http://jeffr-tech.livejournal.com/5705.html >> >> Hardware is an 8-core amd64 system and jeffr seems willing to try more >> >> Linux versions on that machine. >> >> Anyway, is there anyone who can reproduce this? >> > >> > >> > I have reproduced it on a quad core test system. >> > >> > With 4 threads (on 4 cores) I get a high throughput, with >> > approximately 58% user time and 42% system time. >> > >> > With 8 threads (on 4 cores) I get way lower throughput, >> > with 37% user time, 29% system time 35% idle time! >> > >> > The maximum time taken per query also increases from >> > 0.0096s to 0.5273s. Ouch! >> > >> > I don't know if this is MySQL, glibc or Linux kernel, >> > but something strange is going on... >> >> Like you, I'm also seeing idle time start going up as threads increase. >> >> I initially thought this was a problem with the multiprocessor scheduler, >> because the pattern is exactly like some artificat in the load balancing. >> >> However, after looking at the stats, and testing a couple of things, I >> think it may not be after all. >> >> I've reproduced this on a 8-socket/16-way dual core Opteron. So far what >> I am seeing is that MySQL is having trouble putting enough load into the >> scheduler. > > > Here are some graphs from the 4-socket/8-way Xeon box (no SMT, no MC > in .config) I posted about earlier. > > transactions.png resembles Nick's results pretty closely, in that a > drop-off occurs, at the same # of threads, too. That seems weird to > me, but I haven't thought about it too closely. Shouldn't Nick's be > dropping off closer to 16 threads (that would be 1 per core, then, > right?) I don't think it is exactly a matter of processes >= cores, but rather just a general problem at higher concurrency. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com