Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263178AbUDSGNE (ORCPT ); Mon, 19 Apr 2004 02:13:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263335AbUDSGNE (ORCPT ); Mon, 19 Apr 2004 02:13:04 -0400 Received: from smtp103.mail.sc5.yahoo.com ([66.163.169.222]:15442 "HELO smtp103.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S263178AbUDSGNA (ORCPT ); Mon, 19 Apr 2004 02:13:00 -0400 Message-ID: <40836DE8.5080303@yahoo.com.au> Date: Mon, 19 Apr 2004 16:12:56 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040401 Debian/1.6-4 X-Accept-Language: en MIME-Version: 1.0 To: Andrew Morton CC: piotr@larroy.com, linux-kernel@vger.kernel.org Subject: Re: CFQ iosched praise: good perfomance and better latency References: <20040419005651.GA7860@larroy.com> <40835F4E.5000308@yahoo.com.au> <20040418225752.56d10695.akpm@osdl.org> In-Reply-To: <20040418225752.56d10695.akpm@osdl.org> 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 Content-Length: 1426 Lines: 38 Andrew Morton wrote: > Nick Piggin wrote: > >>Pedro Larroy wrote: >> >>>Hi >>> >>>I've been trying CFQ ioscheduler in my software raid5 with nice results, >>>I've observed that a latency pattern still exists, just as in the >>>anticipatory ioscheduler, but those spikes are now much lower (from >>>6ms with AS to 2ms with CFQ as seen in the bottom of >>>http://pedro.larroy.com/devel/iolat/analisys/), >>>plus apps seems to get a fair amount of io so they don't get starved. >>> >>>Seems a good choice for io loaded boxes. Thanks Jens Axboe. >>> >> >>Although AS isn't at its best when behind raid devices (it should >>probably be in front of them), you could be seeing some problem >>with the raid code. >> >>I'd be interested to see what the graph looks like with elevator=noop > > > This isn't a very surprising result, is it? AS throws away latency to gain > throughput. Pedro is measuring latency... > Well I think Pedro actually means *seconds*, not ms. The URL shows AS peaks at nearly 10 seconds latency, and CFQ over 2s. It really seems like a raid problem though, because latency measured at the individual devices is under 250ms for AS. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/