Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752574AbZCBNNY (ORCPT ); Mon, 2 Mar 2009 08:13:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751276AbZCBNNQ (ORCPT ); Mon, 2 Mar 2009 08:13:16 -0500 Received: from brick.kernel.dk ([93.163.65.50]:57874 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750920AbZCBNNP (ORCPT ); Mon, 2 Mar 2009 08:13:15 -0500 Date: Mon, 2 Mar 2009 14:13:13 +0100 From: Jens Axboe To: ???? Cc: linux-kernel@vger.kernel.org Subject: Re: The difference of request dir between AS and Deadline I/O scheduler? Message-ID: <20090302131313.GU11787@kernel.dk> References: <20090302122547.GT11787@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1824 Lines: 60 On Mon, Mar 02 2009, ???? wrote: > Do you mean that the same process tends to have the same behavior of > I/O in the way of sycn? > Does this mean AS works better when requests are distincted by sync > mode (the success rate of anticipation is higher when requests are > grouped by the mode of sync)? Please don't top post, put your reply beneath the text you are replying to. It means that there's a key distinction between requests. Sync requests often have dependencies on each other, and AS thus enables idling for these types of requests. Async io is usually background activity. I don't understand what you mean by higher success rate. Anticipation is only for sync requests. The grouping is done because it makes behavioural sense. > > Thanks, > > > On Mon, Mar 2, 2009 at 8:25 PM, Jens Axboe wrote: > > On Mon, Mar 02 2009, ???? wrote: > >> Hi, > >> > >> I'm little confused about the defination of request dir in AS and > >> Deadline I/O scheduler. > >> In AS, the request dir is defined by wheher it's sync: > >> > >> data_dir = rq_is_sync(rq); > >> > >> But in Deadline, the requests are grouped by read and write. > >> > >> Why is there the difference since AS is an extension of Deadline? > >> what's the consideration? > > > > Because AS uses the sync vs async distinction to decide whether to > > anticipate a new request from that process. 'sync' is then reads or sync > > writes, whereas deadline does not distinguish between sync and async > > writes. > > > > -- > > Jens Axboe > > > > > > > > -- > Xie Gang -- Jens Axboe -- 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/