From owner-svn-src-head@FreeBSD.ORG Sat Sep 13 20:57:10 2014 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 16C3E344; Sat, 13 Sep 2014 20:57:10 +0000 (UTC) Received: from mail.turbocat.net (heidi.turbocat.net [88.198.202.214]) (using TLSv1.1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id C6CF7972; Sat, 13 Sep 2014 20:57:09 +0000 (UTC) Received: from laptop015.home.selasky.org (cm-176.74.213.204.customer.telag.net [176.74.213.204]) (using TLSv1 with cipher ECDHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by mail.turbocat.net (Postfix) with ESMTPSA id 15E441FE027; Sat, 13 Sep 2014 22:57:07 +0200 (CEST) Message-ID: <5414AF97.50509@selasky.org> Date: Sat, 13 Sep 2014 22:56:55 +0200 From: Hans Petter Selasky User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Rick Macklem Subject: Re: svn commit: r271504 - in head/sys: dev/oce dev/vmware/vmxnet3 dev/xen/netfront net netinet ofed/drivers/net/mlx4 References: <1935263641.35880661.1410641648947.JavaMail.root@uoguelph.ca> In-Reply-To: <1935263641.35880661.1410641648947.JavaMail.root@uoguelph.ca> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Adrian Chadd X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 13 Sep 2014 20:57:10 -0000 On 09/13/14 22:54, Rick Macklem wrote: > Hans Petter Selasky wrote: >> On 09/13/14 22:35, Hans Petter Selasky wrote: >>> >>> I see the default set to (65536 - 4). I don't know why you >>> subtracted 4 >>> but I would have expected the max ethernet header length to be >>> subtracted >>> here? >> >> You mean to say that the default should be >> >> 65535 - ethernet header - vlan header ? >> > Almost. It is actually: > 65536 - ethernet header - vlan header > (or the min of IP_MAXPACKET vs 32*MCLBYTES - ethernet header - vlan header > if you want to cover your butt for the case where the value of > MCLBYTES is changed) IP_MAXPACKET (65535) comes from the fact that > some devices use the iplen field of the ip header in the TSO segment > for its length, I think? (Some do not and can support TSO segments > greater than IP_MAXPACKET in length, but again, the default shouldn't > assume this nor should it assume the device does the vlan header in > hardware --> "- vlan header" to be safe for default.) > > This is because there are lots of broken drivers (basically any one > that has a limit of 32 transmit segments) and this at least makes > them work correctly. Unfortunately they still do a lot of m_defrag() > calls for this case, but with a patch like yours, the drivers may > eventually get patched to use the max_frags setting and then avoid > the need to do m_defrag() calls. > > rick Hi Rick, Thanks for shedding light into existing practices. --HPS