From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: weird throughput on write to SATA disk Date: Mon, 13 Oct 2008 23:39:33 +0100 Message-ID: <20081013233933.2ee5a011@lxorguk.ukuu.org.uk> References: <1223925629.3947.7.camel@duo> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:40659 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755587AbYJMWjn (ORCPT ); Mon, 13 Oct 2008 18:39:43 -0400 In-Reply-To: Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Grant Grundler Cc: kenneth johansson , linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, 13 Oct 2008 14:07:15 -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"? > If not, could be issue with how VM writeback is (not) working. Or just mashing up the I/O horribly. Would also be worth turning the CFQ scheduler off or applying Arjan van de Ven's patches to fix the ioprio of the kernel writeout threads. That last patch makes a huge difference here. Alan