From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sat, 11 Aug 2001 07:58:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sat, 11 Aug 2001 07:58:13 -0400 Received: from cc885639-a.flushing1.mi.home.com ([24.182.96.34]:34323 "HELO caesar.lynix.com") by vger.kernel.org with SMTP id ; Sat, 11 Aug 2001 07:58:07 -0400 Date: Sat, 11 Aug 2001 07:59:06 +0000 From: Subba Rao To: Andrew Morton Cc: Linux Kernel Subject: Re: Half Duplex and Zero Copy IP Message-ID: <20010811075905.A32210@home.com> Reply-To: Subba Rao In-Reply-To: <20010810095313.A6219@home.com> <3B742996.3F2C8DEC@zip.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3B742996.3F2C8DEC@zip.com.au>; from akpm@zip.com.au on Fri, Aug 10, 2001 at 11:36:06AM -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 0, Andrew Morton wrote: > Subba Rao wrote: > > > > Hello, > > > > I have 2 3Com NICs on my system. They are 3c905C Tornado PCI cards. > > The drivers are compiled into the kernel (Slackware 8.0 with kernel 2.4.7). > > > > One of the interfaces will be used as a sniffer interface (without IP address) > > and a very high traffic pipes. I do not wish to loose any packets coming to this > > interface. Is it better if I initialize the interface in HALF DUPLEX mode? If yes, > > how do I set the card to HALF DUPLEX mode? How can I find out the HW (NIC) settings > > on the system? > > No, this will provide no benefit. So, is the card set in half-duplex mode by default and full-duplex is a forced option? > > > Another question about 3Com NICs, do they perform zero-copy IP? > > Linux's zerocopy infrastructure allows the sendfile() system call > to save a copy with NICs which have hardware checksumming and > scatter/gather. 3c905C is one such NIC. Kernel is not generally > "zero copy", but large savings are available in certain situations. > NFS packet reassembly benefits from 905C's as well. > > > I read that the performance improves a lot WITHOUT zero-copy IP. > > Not right. Where did you read that? > http://www.fefe.de/linuxeth/ "To achieve gigabit throughput, it is important that the operating system does not copy the data in the packets before sending them (this is called zero-copy IP). Unfortunately, the kernel needs to put a header before the data in the packet, so not copying the data to a buffer in kernel space means that the NIC needs to be able to fetch the header from a different place in memory than the user data in the packet. This is called scatter/gather and is necessary for zero-copy IP." -- Subba Rao subba9@home.com http://members.home.net/subba9/ GPG public key ID 27FC9217 Key fingerprint = 2B4C 498E 1860 5A2B 6570 5852 7527 882A 27FC 9217