Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932098AbYJMWT0 (ORCPT ); Mon, 13 Oct 2008 18:19:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759428AbYJMWTP (ORCPT ); Mon, 13 Oct 2008 18:19:15 -0400 Received: from 1-1-4-20a.ras.sth.bostream.se ([82.182.72.90]:35250 "EHLO amd.kenjo.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1759233AbYJMWTO (ORCPT ); Mon, 13 Oct 2008 18:19:14 -0400 Subject: Re: weird throughput on write to SATA disk From: kenneth johansson To: Grant Grundler Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: References: <1223925629.3947.7.camel@duo> <1223932956.3947.22.camel@duo> Content-Type: text/plain Date: Tue, 14 Oct 2008 00:19:11 +0200 Message-Id: <1223936351.3947.41.camel@duo> Mime-Version: 1.0 X-Mailer: Evolution 2.24.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1393 Lines: 36 On Mon, 2008-10-13 at 14:34 -0700, Grant Grundler wrote: > On Mon, Oct 13, 2008 at 2:22 PM, kenneth johansson wrote: > > On Mon, 2008-10-13 at 14:07 -0700, Grant Grundler wrote: > >> On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson wrote: > >> > When writing data to /dev/sdb (that is the whole disk and no filesystem) > >> > it starts out ok around 100MB/sec but soon end up doing considerably > >> > worse. For prolonged times lasting several minutes it hovers in the > >> > 20-30MB/sec. > >> > >> Is the application using "O_DIRECT"? > > > > no just open then write no fancy stuff > > > >> If not, could be issue with how VM writeback is (not) working. > > > > the access pattern is the simplest possible. Is there any knobs I could > > try to adjust. > > > >> Can you reproduce this using fio or even "dd"? > >> (See git://git.kernel.dk/fio) > > > > dd is having the same effect. > > Can you try "dd oflag=direct if=/dev/null of=/dev/sdb bs=64k"? I changed to use O_DIRECT and it's much more consistent now. 69-75 with 74 about 95% of the time. the disk is supposed to have 105 115 sustained data rate. -- 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/