From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264959AbUGGRAz (ORCPT ); Wed, 7 Jul 2004 13:00:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265226AbUGGRAz (ORCPT ); Wed, 7 Jul 2004 13:00:55 -0400 Received: from umhlanga.stratnet.net ([12.162.17.40]:46926 "EHLO umhlanga.STRATNET.NET") by vger.kernel.org with ESMTP id S264959AbUGGRAy (ORCPT ); Wed, 7 Jul 2004 13:00:54 -0400 To: Helge Hafting Cc: Davide Rossetti , linux-kernel@vger.kernel.org Subject: Re: MSI to memory? X-Message-Flag: Warning: May contain useful information References: <200407011215.59723.bjorn.helgaas@hp.com> <20040701115339.A4265@unix-os.sc.intel.com> <40EBED33.3050707@roma1.infn.it> <40EBF07B.8040003@hist.no> From: Roland Dreier Date: Wed, 07 Jul 2004 09:59:14 -0700 In-Reply-To: <40EBF07B.8040003@hist.no> (Helge Hafting's message of "Wed, 07 Jul 2004 14:45:47 +0200") Message-ID: <52vfgzoisd.fsf@topspin.com> User-Agent: Gnus/5.1006 (Gnus v5.10.6) XEmacs/21.4 (Security Through Obscurity, linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-OriginalArrivalTime: 07 Jul 2004 16:59:14.0431 (UTC) FILETIME=[BB7CA0F0:01C46443] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Helge> Won't that put a bad load on the bus? Someone else might Helge> need it: * Another cpu in a smp system * Any device doing Helge> bus-master transfers, even in a UP system Actually with MSI, the PCI device writes directly to a host address. In the proposed usage in this mail thread, the address is in host memory, so there's no bus load to poll the memory. Presumably the memory will be pulled into cache for the duration of the poll loop, so there's not even any memory bandwidth consumed. (Of course this only works on an architecture where PCI DMA is cache coherent) - Roland Date: Wed, 07 Jul 2004 09:59:04 -0700 In-Reply-To: <40EBF07B.8040003@hist.no> (Helge Hafting's message of "Wed, 07 Jul 2004 14:45:47 +0200") Message-ID: <52wu1foisn.fsf@topspin.com> User-Agent: Gnus/5.1006 (Gnus v5.10.6) XEmacs/21.4 (Security Through Obscurity, linux)