From owner-freebsd-net@freebsd.org Wed Aug 19 07:52:34 2015 Return-Path: Delivered-To: freebsd-net@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id EB7139BDF9E; Wed, 19 Aug 2015 07:52:34 +0000 (UTC) (envelope-from hps@selasky.org) Received: from mail.turbocat.net (heidi.turbocat.net [88.198.202.214]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id A967BF8E; Wed, 19 Aug 2015 07:52:34 +0000 (UTC) (envelope-from hps@selasky.org) Received: from laptop015.home.selasky.org (cm-176.74.213.204.customer.telag.net [176.74.213.204]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.turbocat.net (Postfix) with ESMTPSA id 6EE091FE023; Wed, 19 Aug 2015 09:52:32 +0200 (CEST) Subject: Re: ix(intel) vs mlxen(mellanox) 10Gb performance To: pyunyh@gmail.com References: <1D52028A-B39F-4F9B-BD38-CB1D73BF5D56@cs.huji.ac.il> <17871443-E105-4434-80B1-6939306A865F@cs.huji.ac.il> <473274181.23263108.1439814072514.JavaMail.zimbra@uoguelph.ca> <7F892C70-9C04-4468-9514-EDBFE75CF2C6@cs.huji.ac.il> <805850043.24018217.1439848150695.JavaMail.zimbra@uoguelph.ca> <9D8B0503-E8FA-43CA-88F0-01F184F84D9B@cs.huji.ac.il> <1721122651.24481798.1439902381663.JavaMail.zimbra@uoguelph.ca> <55D333D6.5040102@selasky.org> <1325951625.25292515.1439934848268.JavaMail.zimbra@uoguelph.ca> <55D429A4.3010407@selasky.org> <20150819074212.GB964@michelle.fasterthan.com> Cc: Rick Macklem , FreeBSD stable , FreeBSD Net , Slawa Olhovchenkov , Christopher Forgeron , Daniel Braniss From: Hans Petter Selasky Message-ID: <55D43615.1030401@selasky.org> Date: Wed, 19 Aug 2015 09:53:57 +0200 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <20150819074212.GB964@michelle.fasterthan.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Aug 2015 07:52:35 -0000 On 08/19/15 09:42, Yonghyeon PYUN wrote: > On Wed, Aug 19, 2015 at 09:00:52AM +0200, Hans Petter Selasky wrote: >> On 08/18/15 23:54, Rick Macklem wrote: >>> Ouch! Yes, I now see that the code that counts the # of mbufs is before the >>> code that adds the tcp/ip header mbuf. >>> >>> In my opinion, this should be fixed by setting if_hw_tsomaxsegcount to >>> whatever >>> the driver provides - 1. It is not the driver's responsibility to know if >>> a tcp/ip >>> header mbuf will be added and is a lot less confusing that expecting the >>> driver >>> author to know to subtract one. (I had mistakenly thought that >>> tcp_output() had >>> added the tc/ip header mbuf before the loop that counts mbufs in the list. >>> Btw, >>> this tcp/ip header mbuf also has leading space for the MAC layer header.) >>> >> >> Hi Rick, >> >> Your question is good. With the Mellanox hardware we have separate >> so-called inline data space for the TCP/IP headers, so if the TCP stack >> subtracts something, then we would need to add something to the limit, >> because then the scatter gather list is only used for the data part. >> > > I think all drivers in tree don't subtract 1 for > if_hw_tsomaxsegcount. Probably touching Mellanox driver would be > simpler than fixing all other drivers in tree. > >> Maybe it can be controlled by some kind of flag, if all the three TSO >> limits should include the TCP/IP/ethernet headers too. I'm pretty sure >> we want both versions. >> > > Hmm, I'm afraid it's already complex. Drivers have to tell almost > the same information to both bus_dma(9) and network stack. Don't forget that not all drivers in the tree set the TSO limits before if_attach(), so possibly the subtraction of one TSO fragment needs to go into ip_output() .... --HPS