Date: Wed, 19 Aug 2015 09:53:57 +0200 From: Hans Petter Selasky <hps@selasky.org> To: pyunyh@gmail.com Cc: Rick Macklem <rmacklem@uoguelph.ca>, FreeBSD stable <freebsd-stable@freebsd.org>, FreeBSD Net <freebsd-net@freebsd.org>, Slawa Olhovchenkov <slw@zxy.spb.ru>, Christopher Forgeron <csforgeron@gmail.com>, Daniel Braniss <danny@cs.huji.ac.il> Subject: Re: ix(intel) vs mlxen(mellanox) 10Gb performance Message-ID: <55D43615.1030401@selasky.org> In-Reply-To: <20150819074212.GB964@michelle.fasterthan.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>
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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
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