Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261355AbTIKQZK (ORCPT ); Thu, 11 Sep 2003 12:25:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261356AbTIKQZK (ORCPT ); Thu, 11 Sep 2003 12:25:10 -0400 Received: from parcelfarce.linux.theplanet.co.uk ([195.92.249.252]:8374 "EHLO www.linux.org.uk") by vger.kernel.org with ESMTP id S261355AbTIKQZF (ORCPT ); Thu, 11 Sep 2003 12:25:05 -0400 Date: Thu, 11 Sep 2003 17:25:04 +0100 From: Matthew Wilcox To: Andi Kleen Cc: Matthew Wilcox , linux-kernel@vger.kernel.org Subject: Re: Memory mapped IO vs Port IO Message-ID: <20030911162504.GL21596@parcelfarce.linux.theplanet.co.uk> References: <20030911160116.GI21596@parcelfarce.linux.theplanet.co.uk.suse.lists.linux.kernel> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1017 Lines: 20 On Thu, Sep 11, 2003 at 06:17:02PM +0200, Andi Kleen wrote: > The overhead of checking for PIO vs mmio at runtime in the drivers > should be completely in the noise on any non ancient CPU (both MMIO > and PIO typically take hundreds or thousands of CPU cycles for the bus > access, having an dynamic function call or an if before that is makes > no difference at all) That's not true for MMIO writes which are posted. They should take no longer than a memory write. For MMIO reads and PIO reads & writes, you are, of course, correct. -- "It's not Hollywood. War is real, war is primarily not about defeat or victory, it is about death. I've seen thousands and thousands of dead bodies. Do you think I want to have an academic debate on this subject?" -- Robert Fisk - 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/