From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: RFC [PATCH net-2.6 1/6] net: Scheduling softirqs between CPUSs Date: Wed, 12 Mar 2008 15:10:52 +0000 Message-ID: <20080312151051.GI26963@solarflare.com> References: <20080305205116.5989A412541@localhost> <20080305.132112.01598419.davem@davemloft.net> <47D19147.9070609@qualcomm.com> <36D9DB17C6DE9E40B059440DB8D95F52049D5CE5@orsmsx418.amr.corp.intel.com> <65634d660803110920g5103dc60ya055a10f999b4e25@mail.gmail.com> <20080311165253.GG26963@solarflare.com> <65634d660803111648l15c4d653t52b4fc9e8dfa531d@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Brandeburg, Jesse" , Max Krasnyanskiy , David Miller , netdev@vger.kernel.org, Steven Rostedt , Ingo Molnar To: Tom Herbert Return-path: Received: from pythagoras.zen.co.uk ([212.23.3.140]:59257 "EHLO pythagoras.zen.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751752AbYCLPLG (ORCPT ); Wed, 12 Mar 2008 11:11:06 -0400 Content-Disposition: inline In-Reply-To: <65634d660803111648l15c4d653t52b4fc9e8dfa531d@mail.gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: Tom Herbert wrote: > > Recent versions of Windows that are aware of RSS will instruct network > > drivers to update their RSS indirection tables so that received > > packets are handled on the same CPU as the thread likely to use the > > received data. This requires that the network stack knows the hash > > function, so Microsoft specified a "Toeplitz hash" for IPv4 and IPv6. > > You can expect that most hardware RSS implementations will use this > > function and not a simple XOR. > > > > Thanks. I am planning to do the Toeplitz hash in the softRSS. Also, > I was planning to add support for devices that provide the Toeplitz > hash but don't do full RSS. > > One nice feature about Microsoft RSS seems to be the ability for the > stack to dynamically re-balance networking load of a device using > an indirection table that is set up in the device. I was wondering if > this is supported in Linux stack or if anyone is working on that? It's not supported, but it's on David Miller's to-do list[1]. By the way, Microsoft suddenly decided that RSS is too problematic to enable by default[2] because software and hardware can disagree about hash values in the presence of some local NAT implementations. Hopefully we can avoid that particular pitfall in Linux. Ben. 1. http://vger.kernel.org/~davem/net_todo.html 2. http://support.microsoft.com/kb/948496 -- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job.