From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 27 May 2002 04:19:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 27 May 2002 04:19:25 -0400 Received: from parcelfarce.linux.theplanet.co.uk ([195.92.249.252]:18183 "EHLO www.linux.org.uk") by vger.kernel.org with ESMTP id ; Mon, 27 May 2002 04:19:24 -0400 Message-ID: <3CF1ECD1.A1BB2CF1@zip.com.au> Date: Mon, 27 May 2002 01:22:41 -0700 From: Andrew Morton X-Mailer: Mozilla 4.79 [en] (X11; U; Linux 2.4.19-pre8 i686) X-Accept-Language: en MIME-Version: 1.0 To: Jens Axboe CC: William Lee Irwin III , Giuliano Pochini , linux-kernel@vger.kernel.org, "chen, xiangping" Subject: Re: Poor read performance when sequential write presents In-Reply-To: <3CED4843.2783B568@zip.com.au> <3CEE0758.27110CAD@zip.com.au> <20020524094606.GH14918@holomorphy.com> <3CEE1035.1E67E1B8@zip.com.au> <20020527080632.GC17674@suse.de> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jens Axboe wrote: > > ... > > But in 2.5, head-activeness went away and as far as I know, IDE and SCSI are > > treated the same. Odd. > > It didn't really go away, it just gets handled automatically now. > elv_next_request() marks the request as started, in which case the i/o > scheduler won't consider it for merging etc. SCSI removes the request > directly after it has been marked started, while IDE leaves it on the > queue until it completes. For IDE TCQ, the behaviour is the same as with > SCSI. It won't consider the active request at the head of the queue for merging (making the request larger). But it _could_ consider the request when making decisions about insertion (adding a new request at the head of the queue because it's close-on-disk to the active one). Does it do that? -