Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753997AbYJBPV4 (ORCPT ); Thu, 2 Oct 2008 11:21:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752599AbYJBPVt (ORCPT ); Thu, 2 Oct 2008 11:21:49 -0400 Received: from mail-in-16.arcor-online.net ([151.189.21.56]:41878 "EHLO mail-in-16.arcor-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752414AbYJBPVs (ORCPT ); Thu, 2 Oct 2008 11:21:48 -0400 From: Bodo Eggert <7eggert@gmx.de> Subject: Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority To: Jens Axboe , Dave Chinner , Andi Kleen , Andrew Morton , Arjan van de Ven , linux-kernel@vger.kernel.org, Alan Cox Reply-To: 7eggert@gmx.de Date: Thu, 02 Oct 2008 17:32:04 +0200 References: User-Agent: KNode/0.10.4 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7Bit Message-Id: X-be10.7eggert.dyndns.org-MailScanner-Information: See www.mailscanner.info for information X-be10.7eggert.dyndns.org-MailScanner: Found to be clean X-be10.7eggert.dyndns.org-MailScanner-From: 7eggert@gmx.de Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1316 Lines: 22 Jens Axboe wrote: > On Thu, Oct 02 2008, Dave Chinner wrote: >> On Thu, Oct 02, 2008 at 09:55:11AM +0200, Jens Axboe wrote: >> > Good point. I think we should mark the IO as sync, and maintain the same >> > priority level. Any IO that ends up being waited on is sync by >> > definition, we just need to expand the coverage a bit. >> >> That's what XFS has always done - mark the journal I/O as sync. >> Still, once you load up the elevator, the sync I/O can still get >> delayed for hundreds of milliseconds before dispatch, which was >> why I started looking at boosting the priority of the log I/O. >> It proved to be much more effective at getting the log I/O >> dispatched than the existing "mark it sync" technique.... > > Sure, just marking it as sync is not a magic bullet. It'll be in the > first priority for that class, but it'll share bandwidth with other > processes. So if you have lots of IO going on, it can take hundreds of > miliseconds before being dispatched. Sounds like you need a priority class besides sync and async. -- 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/