From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934839AbXJOUQt (ORCPT ); Mon, 15 Oct 2007 16:16:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763961AbXJOUQh (ORCPT ); Mon, 15 Oct 2007 16:16:37 -0400 Received: from mx1.redhat.com ([66.187.233.31]:54043 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752853AbXJOUQf (ORCPT ); Mon, 15 Oct 2007 16:16:35 -0400 Date: Mon, 15 Oct 2007 16:13:15 -0400 From: Rik van Riel To: Andrew Morton Cc: Arjan van de Ven , linux-kernel@vger.kernel.org, jens.axboe@oracle.com, mingo@elte.hu Subject: Re: [patch] Give kjournald a IOPRIO_CLASS_RT io priority Message-ID: <20071015161315.4fe18e07@bree.surriel.com> In-Reply-To: <20071015114738.6b5a25c7.akpm@linux-foundation.org> References: <20071015104647.14e60bc5@laptopd505.fenrus.org> <20071015114738.6b5a25c7.akpm@linux-foundation.org> Organization: Red Hat, Inc. X-Mailer: Claws Mail 2.9.1 (GTK+ 2.10.4; x86_64-redhat-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, 15 Oct 2007 11:47:38 -0700 Andrew Morton wrote: > On Mon, 15 Oct 2007 10:46:47 -0700 > Arjan van de Ven wrote: > > > > > Subject: Give kjournald a IOPRIO_CLASS_RT io priority > > From: Arjan van de Ven > Seems a pretty fundamental change which could do with some careful > benchmarking, methinks. FWIW, I have marked the kjournald processes on my system realtime with "rtprio -c 1 `pidof kjournald`" and the usual desktop stalls that plague my system have not yet happened this afternoon. > See, your patch amounts to "do more seeks to improve one test case". > Surely other testcases will worsen. What are they? The big problem I have seen here is that processes end up waiting on kjournald to do something, and kjournald is waiting due to the IO scheduler. This can cause a lot of low IO (high IO priority) processes to indirectly get stuck behind a few high IO (low priority) processes. Since you have been involved a lot with ext3 development, which kinds of workloads do you think will show a performance degradation with Arjan's patch? What should I test? -- "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." - Brian W. Kernighan