From owner-cvs-all Tue Jul 27 8:15: 8 1999 Delivered-To: cvs-all@freebsd.org Received: from dingo.cdrom.com (castles554.castles.com [208.214.165.118]) by hub.freebsd.org (Postfix) with ESMTP id 68B12153D4; Tue, 27 Jul 1999 08:15:04 -0700 (PDT) (envelope-from mike@dingo.cdrom.com) Received: from dingo.cdrom.com (LOCALHOST [127.0.0.1]) by dingo.cdrom.com (8.9.3/8.8.8) with ESMTP id IAA03379; Tue, 27 Jul 1999 08:10:29 -0700 (PDT) (envelope-from mike@dingo.cdrom.com) Message-Id: <199907271510.IAA03379@dingo.cdrom.com> X-Mailer: exmh version 2.0.2 2/24/98 To: Brian Somers Cc: 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 10:01:12 BST." <199907270901.KAA01833@keep.lan.Awfulhak.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Tue, 27 Jul 1999 08:10:29 -0700 From: Mike Smith 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. ... > 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. Well, no, that's just it; if you are on a must-be-aligned architecture, you start with the payload already aligned, so no matter what the ensuing encapsulation it stays aligned. -- \\ The mind's the standard \\ Mike Smith \\ of the man. \\ msmith@freebsd.org \\ -- Joseph Merrick \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message