Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266683AbUIANYo (ORCPT ); Wed, 1 Sep 2004 09:24:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266689AbUIANYI (ORCPT ); Wed, 1 Sep 2004 09:24:08 -0400 Received: from cpu1185.adsl.bellglobal.com ([207.236.110.166]:4992 "EHLO mail.rtr.ca") by vger.kernel.org with ESMTP id S266555AbUIANWD (ORCPT ); Wed, 1 Sep 2004 09:22:03 -0400 Message-ID: <4135CC9E.5060905@rtr.ca> Date: Wed, 01 Sep 2004 09:20:30 -0400 From: Mark Lord User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040803 X-Accept-Language: en, en-us MIME-Version: 1.0 To: bzolnier@milosz.na.pl Cc: Lee Revell , Greg Stark , Denis Vlasenko , Alan Cox , Todd Poynor , Linux Kernel Mailing List , tim.bird@am.sony.com, dsingleton@mvista.com Subject: Re: [PATCH] Configure IDE probe delays References: <20040730191100.GA22201@slurryseal.ddns.mvista.com> <200408272005.08407.bzolnier@elka.pw.edu.pl> <1093630121.837.39.camel@krustophenia.net> <200408272059.51779.bzolnier@elka.pw.edu.pl> In-Reply-To: <200408272059.51779.bzolnier@elka.pw.edu.pl> 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: 1186 Lines: 32 Bartlomiej Zolnierkiewicz wrote: > >>What determines whether 48 bit addressing will be used then? > > Availability of 48-bit addressing feature set and host capabilities > (some don't support LBA48 when DMA is used etc.). I haven't examined the "released" IDE drivers in some time, but one optimisation that can save a LOT of CPU usage is for the driver to only use LBA48 *when necessary*, and use LBA28 I/O otherwise. Each access to an IDE register typically chews up 600+ns, or the equivalent of a couple thousand instruction executions on a modern core. Avoiding LBA48 when it's not needed will save four such accesses per I/O, or about 2.5us. LBA48 is only needed when (1) the sector count is greater than 256, and/or (2) the ending sector number >= (1<<28). I regularly include this optimisation in the drivers I have been working on since LBA48 first appeared. Cheers -- Mark Lord (hdparm keeper & the original "Linux IDE Guy") - 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/