Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267427AbUIATgz (ORCPT ); Wed, 1 Sep 2004 15:36:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267429AbUIATgz (ORCPT ); Wed, 1 Sep 2004 15:36:55 -0400 Received: from viper.oldcity.dca.net ([216.158.38.4]:3046 "HELO viper.oldcity.dca.net") by vger.kernel.org with SMTP id S267427AbUIATgv (ORCPT ); Wed, 1 Sep 2004 15:36:51 -0400 Subject: Re: [PATCH] Configure IDE probe delays From: Lee Revell To: Mark Lord Cc: Jeff Garzik , bzolnier@milosz.na.pl, Greg Stark , Denis Vlasenko , Alan Cox , Todd Poynor , Linux Kernel Mailing List , tim.bird@am.sony.com, dsingleton@mvista.com In-Reply-To: <4135EC84.6070407@rtr.ca> 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> <4135CC9E.5060905@rtr.ca> <4135E017.1000901@pobox.com> <4135EC84.6070407@rtr.ca> Content-Type: text/plain Message-Id: <1094067412.1970.48.camel@krustophenia.net> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 Date: Wed, 01 Sep 2004 15:36:53 -0400 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1267 Lines: 29 On Wed, 2004-09-01 at 11:36, Mark Lord wrote: > With good ADMA or host-queuing controllers that access system > memory directly for their command blocks, then there's not much > (if any) penalty for the extra LBA48 setup. But for "normal" > controllers (if such a beast even exists), the extra writes across > the PCI bus can be costly. > > Hardware write-buffer FIFOs between the CPU and the PCI bus > can reduce the impact of this somewhat, but they are often > only 2-4 entries deep, and will be filled by a normal (S)ATA > command setup sequence. > > This is one of those finer points that is very difficult to measure, > since the I/O throughput is pretty much unaffected by it. But CPU > cycle count per-I/O setup is one way to measure it. > The effect can be measured using a recent version of the voluntary preemption patches, and disabling hardirq preemption. In this situation the IDE I/O completion is by far the longest non-preemptible code path, so can be easily profiled from the latency traces. Lee - 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/