Date: Sat, 29 Sep 2001 12:00:59 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: "Kenneth D. Merry" <ken@kdm.org> Cc: Jonathan Lemon <jlemon@flugsvamp.com>, the_srinivas@hotmail.com, hackers@FreeBSD.ORG Subject: Re: TCP&IP cksum offload on FreeBSD 4.2 Message-ID: <3BB61A6B.A97E955A@mindspring.com> References: <200109270157.f8R1vZ546863@prism.flugsvamp.com> <3BB42E50.B32F5E95@mindspring.com> <20010928074347.A36960@panzer.kdm.org>
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"Kenneth D. Merry" wrote: [ ... transmit checksum offload ... ] > You've got things confused. I think that may be a limitation of some > SysKonnect boards, but certainly isn't a Tigon limitation. Yes, it's not Tigon chipset specific. > Tigon boards come with 512KB, 1MB, or 2MB (never seen one of these) of SRAM > on board. The firmware takes a couple hundred KB, so you generally have at > least 200KB, and possibly a good bit more for packet storage space on the > card. > > So there is buffer space for a number of packets on both the send and > receive sides, and checksumming works in both directions. This depends on the driver division of memory; fortunately, the FreeBSD driver is OK in this regard. > > Also note that this card is not known to be the fastest > > one ot there, so you may be better off doing the checksum > > on your 1GHz+ host processor instead. > > You can get wire rate with a Tigon 2 board, with jumbo frames at least. > (That's with checksum offloading enabled.) Unfortunately, it can not correctly interoperate with a number of cards in jumbogram mode, so unless you know the card on the other end and manually configure it (it can't negotiate properly), you can't really use jumbograms. Or you could rewrite the firmware (of course). I have never seen the board with the stock FreeBSD driver get better than about half wire rate with normal size packets and window depth. On the other hand, the Tigon III is capable of 960 megabits -- about the wire rate limit -- with normal size packets, if you implement software interrupt coelescing (which doesn't help, unless you crank the load up to close to wire speed and/or do more of the stack processing at interrupt time). The Tigon II also has the unfortunate need to download its firmware, and a FreeBSD bug -- the lack of a distinct state for firmware download -- means that the firmware get sent to the card each time the thing is config'ed up, or an IP alias is added to the thing. Plus the damn things are more expensive than the Tigon III based cards. To put a final nail in the coffin, the card can't offload TCP checksum with VLANs enabled (it breaks). All in all, the Tigon II is a bad board. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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