From owner-freebsd-net@FreeBSD.ORG Tue Aug 1 12:41:07 2006 Return-Path: X-Original-To: net@FreeBSD.org Delivered-To: freebsd-net@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 3A14F16A4DD; Tue, 1 Aug 2006 12:41:07 +0000 (UTC) (envelope-from gallatin@cs.duke.edu) Received: from duke.cs.duke.edu (duke.cs.duke.edu [152.3.140.1]) by mx1.FreeBSD.org (Postfix) with ESMTP id AE87943D46; Tue, 1 Aug 2006 12:41:06 +0000 (GMT) (envelope-from gallatin@cs.duke.edu) Received: from grasshopper.cs.duke.edu (grasshopper.cs.duke.edu [152.3.145.30]) by duke.cs.duke.edu (8.13.6/8.13.6) with ESMTP id k71Cf5ll028998 (version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO); Tue, 1 Aug 2006 08:41:05 -0400 (EDT) Received: (from gallatin@localhost) by grasshopper.cs.duke.edu (8.12.9p2/8.12.9/Submit) id k71Cf0NH061024; Tue, 1 Aug 2006 08:41:00 -0400 (EDT) (envelope-from gallatin) From: Andrew Gallatin MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17615.19420.172545.986872@grasshopper.cs.duke.edu> Date: Tue, 1 Aug 2006 08:41:00 -0400 (EDT) To: Robert Watson In-Reply-To: <20060730141642.D16341@fledge.watson.org> References: <20060730141642.D16341@fledge.watson.org> X-Mailer: VM 6.75 under 21.1 (patch 12) "Channel Islands" XEmacs Lucid Cc: arch@FreeBSD.org, net@FreeBSD.org Subject: Re: Changes in the network interface queueing handoff model X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 01 Aug 2006 12:41:07 -0000 Robert Watson writes: > The immediate practical benefit is > clear: if the queueing at the ifnet layer is unnecessary, it is entirely > avoided, skipping enqueue, dequeue, and four mutex operations. This is indeed nice, but for TCP I think the benefit would be far greater if somebody would PLEASE, PLEASE, PLEASE implement TSO (aka LSO). Consider a 1460 byte mss and 64KB of data that is ready to be sent. With the current model, that is 45 separate calls to if_output(), and 45*4 (queuing) + 45 (tx routine) == 225 mutex operations. Using your model, we're down to 45 mutex operations. Using TSO, we have 4 + 1 == 5 mutex operations with the old model, and 1 with the your model. This is not even considering all the other overhead involved in 45 transmits vs TSO... Just something to think about.. Drew