From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261320AbTDMR4e (for ); Sun, 13 Apr 2003 13:56:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261329AbTDMR4e (for ); Sun, 13 Apr 2003 13:56:34 -0400 Received: from siaag2ab.compuserve.com ([149.174.40.132]:36316 "EHLO siaag2ab.compuserve.com") by vger.kernel.org with ESMTP id S261320AbTDMR4d (for ); Sun, 13 Apr 2003 13:56:33 -0400 Date: Sun, 13 Apr 2003 14:03:41 -0400 From: Chuck Ebbert <76306.1226@compuserve.com> Subject: Re: Benefits from computing physical IDE disk geometry? To: Nick Piggin Cc: linux-kernel Message-ID: <200304131407_MC3-1-3441-57C7@compuserve.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote: >> >> Any good SCSI drive knows the physical geometry of the disk and can >> therefore optimally schedule reads and writes. Although necessary features, >> like read queueing, are also available in the current SATA spec, I'm not >> sure most drives will implement it, at least not very well. >> > The "continuous" nature of drive addressing means that the kernel > can do a fine job seek-wise. Due to write caches and read track > buffers, rotational scheduling (which could be done if we knew > geometry) would provide too little gain for the complexity. I would > say that for most workloads you wouldn't see any difference. (IMO) OTOH you can come up with scenarios like, say, a DBMS doing 16K page aligned IO to raw devices where you might see big gains from making sure those 16K chunks didn't cross a physical cylinder boundary. -- Chuck