Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264726AbUJLMTV (ORCPT ); Tue, 12 Oct 2004 08:19:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265051AbUJLMTV (ORCPT ); Tue, 12 Oct 2004 08:19:21 -0400 Received: from ns.virtualhost.dk ([195.184.98.160]:34538 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S264726AbUJLMTS (ORCPT ); Tue, 12 Oct 2004 08:19:18 -0400 Date: Tue, 12 Oct 2004 14:12:28 +0200 From: Jens Axboe To: Nick Piggin Cc: "Ronny V. Vindenes" , ck@vds.kolivas.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: CFQ v2 high cpu load fix(?) Message-ID: <20041012121227.GA1754@suse.de> References: <1097579760.4086.27.camel@tentacle125.gozu.lan> <416BBF48.4070102@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <416BBF48.4070102@yahoo.com.au> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1866 Lines: 52 On Tue, Oct 12 2004, Nick Piggin wrote: > Ronny V. Vindenes wrote: > >CFQ v2 is much better in a lot of cases, but certain situations trigger > >a cpu load so high it starves the rest of the system thus completely > >ruining the interactive experience. While casually looking at the > >problem, I stumbled upon a patch by Arjan van de Ven sent to lkml on > >sept. 1 (Subject: block fixes). Part of it is already included in the > >CFQ v2 patches and after applying the rest[1] I'm no longer able to > >trigger the problem. > > > >[1] Patch attached against 2.6.9-rc4-ck1 but applies to rc4-mm1 with > >some minor fuzz. > > > > > > > >------------------------------------------------------------------------ > > > >--- patches/linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c 2004-10-12 > >12:25:09.798003278 +0200 > >+++ linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c 2004-10-12 > >12:25:42.959479479 +0200 > >@@ -100,7 +100,7 @@ > > nr = q->nr_requests; > > q->nr_congestion_on = nr; > > > >- nr = q->nr_requests - (q->nr_requests / 8) - 1; > >+ nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests/16)- 1; > > if (nr < 1) > > nr = 1; > > q->nr_congestion_off = nr; > > > I thought this first hunk looked like a good idea when Arjan sent the > patch. Can you check if it alone helps your problem? Yeah agree, it's a good idea to leave a bit of air between congestion on and off. Fully explains the cfq v2 excessive sys time for some workloads, which is extra nice. > The second hunk should be basically a noop. I don't see what it is trying to achieve, I like the current code better. -- Jens Axboe - 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/