From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933111AbWF2Xq2 (ORCPT ); Thu, 29 Jun 2006 19:46:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933110AbWF2Xq1 (ORCPT ); Thu, 29 Jun 2006 19:46:27 -0400 Received: from dsl027-180-168.sfo1.dsl.speakeasy.net ([216.27.180.168]:26762 "EHLO sunset.davemloft.net") by vger.kernel.org with ESMTP id S933108AbWF2Xq0 (ORCPT ); Thu, 29 Jun 2006 19:46:26 -0400 Date: Thu, 29 Jun 2006 16:46:23 -0700 (PDT) Message-Id: <20060629.164623.59469884.davem@davemloft.net> To: bos@pathscale.com Cc: 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 From: David Miller In-Reply-To: <1151624063.10886.34.camel@chalcedony.pathscale.com> References: <1151618377.10886.23.camel@chalcedony.pathscale.com> <20060629.150319.104035601.davem@davemloft.net> <1151624063.10886.34.camel@chalcedony.pathscale.com> X-Mailer: Mew version 4.2 on Emacs 21.4 / Mule 5.0 (SAKAKI) 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 From: Bryan O'Sullivan Date: Thu, 29 Jun 2006 16:34:23 -0700 > I'm not quite following you, though I assume you're referring to Niagara > or Rock :-) Are you saying a memcpy_nc would do worse than plain > memcpy, or worse than some other memcpy-like routine? It would do worse than memcpy. 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.