Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 5 Feb 2001 00:16:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 5 Feb 2001 00:15:55 -0500 Received: from pizda.ninka.net ([216.101.162.242]:4745 "EHLO pizda.ninka.net") by vger.kernel.org with ESMTP id ; Mon, 5 Feb 2001 00:15:42 -0500 From: "David S. Miller" MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <14974.13952.347437.536161@pizda.ninka.net> Date: Sun, 4 Feb 2001 21:13:36 -0800 (PST) To: jamal Cc: Rick Jones , Ion Badulescu , Andrew Morton , lkml , "netdev@oss.sgi.com" Subject: Re: Still not sexy! (Re: sendfile+zerocopy: fairly sexy (nothing todowith ECN) In-Reply-To: In-Reply-To: <3A77777D.E1A998FC@cup.hp.com> X-Mailer: VM 6.75 under 21.1 (patch 13) "Crater Lake" XEmacs Lucid Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org jamal writes: > > So, now you have to ask how well any given NIC follows chains of > > buffers. At what number of buffers is the overhead in the NIC of > > following the chains enough to keep it from achieving link-rate? > > > > hmmm... not sure how you would enforce this today or why you would > want that. Alexey, Dave? > The kernel should be able to break it into two buffers(with netperf, > for example -- header + data). > Ok, probably with tux-http 3 (header, data, trailler). First, just to make sure Jamal understands what Rick Jones is trying to make note of. He is trying to say that the cost of dealing with extra TX descriptor ring entries can begin to nullify the gains of zerocopy, depending upon HW implementation (both at the NIC and the PCI controller). Back to today, it is possible that this is an issue if your machine is near PCI bandwidth saturation before zerocopy for these tests. I think this may be one of the factors causing Jamal to see results Alexey cannot reproduce. Get two people with identical PCI host bridges, Acenic in identical PCI slot, I bet the numbers begin to jive. Currently, you get "1 + ((MTU + PAGE_SIZE - 1) / PAGE_SIZE)" buffers per packet when going over a zerocopy device using TCP. Later, David S. Miller davem@redhat.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/