Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263258AbUC3Fy5 (ORCPT ); Tue, 30 Mar 2004 00:54:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263240AbUC3Fy5 (ORCPT ); Tue, 30 Mar 2004 00:54:57 -0500 Received: from 80-169-17-66.mesanetworks.net ([66.17.169.80]:61623 "EHLO mail.bounceswoosh.org") by vger.kernel.org with ESMTP id S261681AbUC3Fyw (ORCPT ); Tue, 30 Mar 2004 00:54:52 -0500 Date: Mon, 29 Mar 2004 22:55:32 -0700 From: "Eric D. Mudama" To: Pavel Machek Cc: Jeff Garzik , linux-ide@vger.kernel.org, Linux Kernel , Andrew Morton Subject: Re: [PATCH] speed up SATA Message-ID: <20040330055532.GA21154@bounceswoosh.org> Mail-Followup-To: Pavel Machek , Jeff Garzik , linux-ide@vger.kernel.org, Linux Kernel , Andrew Morton References: <4066021A.20308@pobox.com> <20040329113641.GE1453@openzaurus.ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20040329113641.GE1453@openzaurus.ucw.cz> User-Agent: Mutt/1.5.5.1+cvs20040105i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1460 Lines: 37 On Mon, Mar 29 at 13:36, Pavel Machek wrote: >32MB is one second if everything goes okay... That will be horrible for latency, right? It'll be somewhere between half a second and 1.5 seconds, depending on how old your hard drive is, all other things being removed from the equation. The media rate of modern IDE drives is about 60MB/s right now, and going up slightly soon. The top SCSI drives are around 85MB/s if I remember correctly. On average, 1s is about right. It becomes a tradeoff between a big hit now and a lot of little hits over time. If you don't expect to have any idle time soon, you're probably better off flushing as big a chunk as possible to free RAM for the upcoming/continuous workload. If you think you might have idle time, the lower MB/s of smaller requests will keep you more granular and improve latency, even though overall work completed per unit time will be slightly lower. For a bursty access pattern, you're probably best off with small requests that fit within the drive's cache, but I don't have any sort of measurable data on this. Most of the OS testing that we're subjected to doesn't attempt large requests. --eric -- Eric D. Mudama edmudama@mail.bounceswoosh.org - 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/