From owner-freebsd-net Wed Jan 24 12:34:41 2001 Delivered-To: freebsd-net@freebsd.org Received: from iguana.aciri.org (iguana.aciri.org [192.150.187.36]) by hub.freebsd.org (Postfix) with ESMTP id 6765337B401 for ; Wed, 24 Jan 2001 12:34:23 -0800 (PST) Received: (from rizzo@localhost) by iguana.aciri.org (8.11.1/8.11.1) id f0OKYNP19344; Wed, 24 Jan 2001 12:34:23 -0800 (PST) (envelope-from rizzo) From: Luigi Rizzo Message-Id: <200101242034.f0OKYNP19344@iguana.aciri.org> Subject: suboptimal mbuf usage In-Reply-To: <200101241918.LAA23469@implode.root.com> from David Greenman at "Jan 24, 2001 11:18:50 am" To: net@freebsd.org Date: Wed, 24 Jan 2001 12:34:23 -0800 (PST) X-Mailer: ELM [version 2.4ME+ PL43 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Hi, i have been looking at how often a packet which is sent to an ethernet driver is split over multiple mbufs, and it seems that this happens for the vast majority of packets -- basically everything above MHLEN goes into two mbufs, and MTU-sized TCP packets end up using 3 or more mbufs. This is on 4.2, and using ttcp to generate traffic, and ipfw which defaults to accept everything. I seem to remember that there was code at least in TCP which tries to leave room for the link and ip headers, but somehow this seems to fail... Has anyone else noticed this behaviour ? cheers luigi ----------------------------------+----------------------------------------- Luigi RIZZO, luigi@iet.unipi.it . ACIRI/ICSI (on leave from Univ. di Pisa) http://www.iet.unipi.it/~luigi/ . 1947 Center St, Berkeley CA 94704 Phone: (510) 666 2927 ----------------------------------+----------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message