From owner-freebsd-net@FreeBSD.ORG  Wed Apr 15 15:59:41 2009
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
Delivered-To: freebsd-net@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id A2053106564A
	for <freebsd-net@freebsd.org>; Wed, 15 Apr 2009 15:59:41 +0000 (UTC)
	(envelope-from renaud@vmware.com)
Received: from smtp-outbound-2.vmware.com (smtp-outbound-2.vmware.com
	[65.115.85.73]) by mx1.freebsd.org (Postfix) with ESMTP id 8EB988FC17
	for <freebsd-net@freebsd.org>; Wed, 15 Apr 2009 15:59:41 +0000 (UTC)
	(envelope-from renaud@vmware.com)
Received: from mailhost2.vmware.com (mailhost2.vmware.com [10.16.67.167])
	by smtp-outbound-2.vmware.com (Postfix) with ESMTP id CC9B451005
	for <freebsd-net@freebsd.org>; Wed, 15 Apr 2009 08:40:20 -0700 (PDT)
Received: from renaud-dev1 (renaud-dev1.eng.vmware.com [10.20.118.23])
	by mailhost2.vmware.com (Postfix) with ESMTP id A7FF58E5DF
	for <freebsd-net@freebsd.org>; Wed, 15 Apr 2009 08:40:20 -0700 (PDT)
Date: Wed, 15 Apr 2009 08:40:31 -0700
From: Renaud Lienhart <renaud@vmware.com>
To: freebsd-net@freebsd.org
Message-ID: <20090415084031.6d149fef@renaud-dev1>
Organization: VMware, Inc.
X-Mailer: Claws Mail 3.6.1 (GTK+ 2.16.1; i486-pc-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Subject: tcp_output() might generate invalid TSO frames
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 15 Apr 2009 15:59:41 -0000

Hi,

We're having trouble virtualizing FreeBSD 7+ on ESX because of an issue
with the stack's TSO implementation: it sometimes generates TSO packets
whose payload size is actually smaller than the MSS.

The faulty logic is described, along with a patch, in PR #132832. It
has been opened for a while now, without any apparent activity, which
is why I'm reaching the mailing list directly.

ESX currently drops these packets as many physical nics are known to
choke on such frames, which effectively limits FreeBSD guests'
performance.
I don't know about other virtualization stacks' behavior.

http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/132832

Thanks for your time,

	Renaud