Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262026AbUC1AVP (ORCPT ); Sat, 27 Mar 2004 19:21:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261987AbUC1AVP (ORCPT ); Sat, 27 Mar 2004 19:21:15 -0500 Received: from smtp017.mail.yahoo.com ([216.136.174.114]:9144 "HELO smtp017.mail.yahoo.com") by vger.kernel.org with SMTP id S262026AbUC1AVI (ORCPT ); Sat, 27 Mar 2004 19:21:08 -0500 Message-ID: <40661A70.3090608@yahoo.com.au> Date: Sun, 28 Mar 2004 10:21:04 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040122 Debian/1.6-1 X-Accept-Language: en MIME-Version: 1.0 To: Andrew Morton CC: jgarzik@pobox.com, linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] speed up SATA References: <4066021A.20308@pobox.com> <40661049.1050004@yahoo.com.au> <20040327160745.7207ff98.akpm@osdl.org> In-Reply-To: <20040327160745.7207ff98.akpm@osdl.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1374 Lines: 35 Andrew Morton wrote: > Nick Piggin wrote: > >> > >> > With this simple patch, the max request size goes from 128K to 32MB... >> > so you can imagine this will definitely help performance. Throughput >> > goes up. Interrupts go down. Fun for the whole family. >> > >> >> Hi Jeff, >> I think 32MB is too much. You incur latency and lose >> scheduling grainularity. I bet returns start diminishing >> pretty quickly after 1MB or so. > > > As far as interactivity and throughput is concerned, the effect of really > big requests will be the same as the effect of permitting _more_ requests. > Namely: more memory can be under readahead or writeback at any particular > point in time. > Not quite, because a single 32MB write might take what? 500ms to complete... and the IO scheduler wants to stop writes after 60ms if there are waiting reads. And writes will be more likely to be submitted as large requests. I think Jeff is right that in theory though, the drivers should just export their capabilities, and the block layer or IO scheduler should decide on the maximum size to actually use. - 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/