From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arjan van de Ven Subject: Re: [GIT PULL] Ext3 latency fixes Date: Sat, 4 Apr 2009 16:33:49 -0700 Message-ID: <20090404163349.20df1208@infradead.org> References: <1238742067-30814-1-git-send-email-tytso@mit.edu> <20090404135719.GA9812@mit.edu> <20090404151649.GE5178@kernel.dk> <20090404173412.GF5178@kernel.dk> <20090404180108.GH5178@kernel.dk> <20090404232222.GA7480@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Jens Axboe , Linus Torvalds , Linux Kernel Developers List , Ext4 Developers List To: Theodore Tso Return-path: Received: from casper.infradead.org ([85.118.1.10]:56983 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830AbZDDXcU (ORCPT ); Sat, 4 Apr 2009 19:32:20 -0400 In-Reply-To: <20090404232222.GA7480@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sat, 4 Apr 2009 19:22:22 -0400 Theodore Tso wrote: > > However, the full latency fixes all the writes are synchronous, so it > must be the case that the delays are caused by the fact that queue is > getting implicitly unplugged after the synchronous write, and the > problem is no longer the mixing of WRITE and WRITE_SYNC requests as > posted in the commit log for 78f707bf. If we remove the automatic > unplug for WRITE_SYNC requests, and add an explicit unplug where it is > needed, that should fix the performance regression for this particular > sqlite test case. removing the unplug is bound to be bad; after all we're waiting on the IO. But maybe it should be "make the unplug a REALLY short time". At least for rotating storage. For non-rotating .. I'd never wait. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org