Received: with ECARTIS (v1.0.0; list netdev); Sun, 15 Dec 2002 10:27:26 -0800 (PST) Received: from trained-monkey.org (IDENT:root@trained-monkey.org [209.217.122.11]) by oss.sgi.com (8.12.5/8.12.5) with SMTP id gBFIRJ3v032027 for ; Sun, 15 Dec 2002 10:27:20 -0800 Received: (from jes@localhost) by trained-monkey.org (8.11.6/8.9.3) id gBFIVFq23347; Sun, 15 Dec 2002 13:31:15 -0500 To: Andrew Morton Cc: "David S. Miller" , jgarzik@pobox.com, linux-kernel@vger.kernel.org, netdev@oss.sgi.com Subject: Re: [RFC][PATCH] net drivers and cache alignment References: <3DF2844C.F9216283@digeo.com> <20021207.153045.26640406.davem@redhat.com> <3DF28748.186AB31F@digeo.com> <3DF28988.93F268EA@digeo.com> From: Jes Sorensen Date: 15 Dec 2002 13:31:15 -0500 In-Reply-To: Andrew Morton's message of "Sat, 07 Dec 2002 15:51:36 -0800" Message-ID: Lines: 21 X-Mailer: Gnus v5.7/Emacs 20.7 X-archive-position: 1378 X-ecartis-version: Ecartis v1.0.0 Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com X-original-sender: jes@trained-monkey.org Precedence: bulk X-list: netdev >>>>> "Andrew" == Andrew Morton writes: Andrew> Andrew Morton wrote: >> Then I am most confused. None of these fields will be put under >> busmastering or anything like that, so what advantage is there in >> spreading them out? Andrew> Oh I see what you want - to be able to pick up all the Andrew> operating fields in a single fetch. Andrew> That will increase the overall cache footprint though. I Andrew> wonder if it's really a net win, over just keeping it small. There's another case where it matters, I guess one could look at it as similar to the SMP case, but between CPU and device. Some devices have producer indices in host memory which they update whenever it receiving a packet. By putting that seperate from TX data structures you avoid the CPU and the NIC fighting over cache lines. Cheers, Jes