From owner-cvs-all Tue Jul 27 8:47:51 1999 Delivered-To: cvs-all@freebsd.org Received: from storm.FreeBSD.org.uk (storm.freebsd.org.uk [194.242.128.198]) by hub.freebsd.org (Postfix) with ESMTP id 01B4D14D87; Tue, 27 Jul 1999 08:47:38 -0700 (PDT) (envelope-from brian@Awfulhak.org) Received: from keep.lan.Awfulhak.org (localhost [127.0.0.1]) by storm.FreeBSD.org.uk (8.9.3/8.9.3) with ESMTP id QAA68107; Tue, 27 Jul 1999 16:47:36 +0100 (BST) (envelope-from brian@Awfulhak.org) Received: from keep.lan.Awfulhak.org (brian@localhost.lan.Awfulhak.org [127.0.0.1]) by keep.lan.Awfulhak.org (8.9.3/8.9.3) with ESMTP id QAA04985; Tue, 27 Jul 1999 16:48:06 +0100 (BST) (envelope-from brian@keep.lan.Awfulhak.org) Message-Id: <199907271548.QAA04985@keep.lan.Awfulhak.org> X-Mailer: exmh version 2.0.2 2/24/98 To: Mike Smith Cc: Matthew Dillon , "Justin T. Gibbs" , cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org Subject: Re: cvs commit: src/release/sysinstall tcpip.c In-reply-to: Your message of "Tue, 27 Jul 1999 01:07:17 PDT." <199907270807.BAA01251@dingo.cdrom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii From: Brian Somers Date: Tue, 27 Jul 1999 16:48:06 +0100 Sender: owner-cvs-all@FreeBSD.ORG Precedence: bulk > > You can blame the 6-byte MAC header for most of the headaches. > > Actually, I blame the way that layered protocol information is prefixed > rather than postfixed in the datagram's wire format. It doesn't strike > me as being at all well designed from a performance perspective > (although mbuf chaining helps a lot). It would be possible to reduce > both copying and checksum overheads by preallocating trailing space in > the buffer based on the down-stack path (or even just a worst-case > assessment of potential buffer growth), and adding an incremental > checksum field. > > But this would make you totally incompatible with everything else, so > let's just forget that line of thought. Of course there's nothing wrong with guessing how much preceeding space might be required and setting up the mbuf with an appropriate unused gap at the front. The user-land mbuf code in ppp does this so that it already has room for the protocol and address & control fields and doesn't have to go off and find another mbuf. It gets a bit muddy on I-must-be-aligned type architectures, but not really much more than it would anyway. > -- > \\ The mind's the standard \\ Mike Smith > \\ of the man. \\ msmith@freebsd.org > \\ -- Joseph Merrick \\ msmith@cdrom.com -- Brian Don't _EVER_ lose your sense of humour ! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message