From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964813AbWF3A2y (ORCPT ); Thu, 29 Jun 2006 20:28:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964817AbWF3A2y (ORCPT ); Thu, 29 Jun 2006 20:28:54 -0400 Received: from palrel11.hp.com ([156.153.255.246]:7064 "EHLO palrel11.hp.com") by vger.kernel.org with ESMTP id S964813AbWF3A2w (ORCPT ); Thu, 29 Jun 2006 20:28:52 -0400 Message-ID: <44A47042.8060203@hp.com> Date: Thu, 29 Jun 2006 17:28:50 -0700 From: Rick Jones User-Agent: Mozilla/5.0 (X11; U; HP-UX 9000/785; en-US; rv:1.6) Gecko/20040304 X-Accept-Language: en-us, en MIME-Version: 1.0 To: David Miller Cc: bos@pathscale.com, akpm@osdl.org, rdreier@cisco.com, mst@mellanox.co.il, openib-general@openib.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH 39 of 39] IB/ipath - use streaming copy in RDMA interrupt handler to reduce packet loss References: <1151618377.10886.23.camel@chalcedony.pathscale.com> <20060629.150319.104035601.davem@davemloft.net> <1151624063.10886.34.camel@chalcedony.pathscale.com> <20060629.164623.59469884.davem@davemloft.net> In-Reply-To: <20060629.164623.59469884.davem@davemloft.net> 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 > If you bypass the L2 cache, it's pointless because the next > agent (PCI controller, CPU thread, etc.) is going to need the > data in the L2 cache. > > It's better in that kind of setup to eat the L2 cache miss overhead in > memcpy since memcpy can usually prefetch and store buffer in order to > absorb some of the L2 miss costs. I thought that most PCI controllers (that is to say the things bridging PCI to the rest of the system) could do prefetching and/or that PCI-X (if not PCI, no idea about PCI-e) cards could issue multiple transactions anyway? rick jones