Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756508AbYGJJEY (ORCPT ); Thu, 10 Jul 2008 05:04:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752317AbYGJJEP (ORCPT ); Thu, 10 Jul 2008 05:04:15 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:48936 "EHLO the-village.bc.nu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752311AbYGJJEP (ORCPT ); Thu, 10 Jul 2008 05:04:15 -0400 Date: Thu, 10 Jul 2008 09:31:09 +0100 From: Alan Cox To: Martin Sustrik Cc: Andrew Morton , Martin Lucina , linux-kernel@vger.kernel.org Subject: Re: Higher than expected disk write(2) latency Message-ID: <20080710093109.46db7c40@the-village.bc.nu> In-Reply-To: <4875C45C.2010901@fastmq.com> References: <20080628121131.GA14181@nodbug.moloch.sk> <20080709222701.8eab4924.akpm@linux-foundation.org> <4875C45C.2010901@fastmq.com> X-Mailer: Claws Mail 3.4.0 (GTK+ 2.12.8; i386-redhat-linux-gnu) Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a Lloegr o'r rhif cofrestru 3798903 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 662 Lines: 14 > What we see is that AIO performs rather bad while we are still > enqueueing more writes (it misses right position on the disk and has to > do superfluous disk revolvings), however, once we stop enqueueing new > write request, those already in the queue are processed swiftly. Which disk scheduler are you using - some of the disk schedulers intentionally delay writes to try and get better block merging. Alan -- 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/