Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261372AbTIKQbk (ORCPT ); Thu, 11 Sep 2003 12:31:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261383AbTIKQbj (ORCPT ); Thu, 11 Sep 2003 12:31:39 -0400 Received: from ns.suse.de ([195.135.220.2]:31184 "EHLO Cantor.suse.de") by vger.kernel.org with ESMTP id S261372AbTIKQbi (ORCPT ); Thu, 11 Sep 2003 12:31:38 -0400 Date: Thu, 11 Sep 2003 18:31:36 +0200 From: Andi Kleen To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org Subject: Re: Memory mapped IO vs Port IO Message-Id: <20030911183136.01dfeb53.ak@suse.de> In-Reply-To: <20030911162504.GL21596@parcelfarce.linux.theplanet.co.uk> References: <20030911160116.GI21596@parcelfarce.linux.theplanet.co.uk.suse.lists.linux.kernel> <20030911162504.GL21596@parcelfarce.linux.theplanet.co.uk> X-Mailer: Sylpheed version 0.8.9 (GTK+ 1.2.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 937 Lines: 23 On Thu, 11 Sep 2003 17:25:04 +0100 Matthew Wilcox wrote: > 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. Even a memory write is tens to hundres of cycles. -Andi - 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/