Date: Fri, 23 Jul 1999 02:29:06 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: mike@smith.net.au (Mike Smith) Cc: mike@smith.net.au, phk@critter.freebsd.dk, jeremyp@gsmx07.alcatel.com.au, cvs-all@FreeBSD.ORG, cvs-committers@FreeBSD.ORG, jkh@FreeBSD.ORG Subject: Re: cvs commit: src/release/sysinstall tcpip.c Message-ID: <199907230029.CAA28046@labinfo.iet.unipi.it> In-Reply-To: <199907230043.RAA03078@dingo.cdrom.com> from "Mike Smith" at Jul 22, 99 05:43:29 pm
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> I forgot to mention that if we bite the bullet and tell ether_input to > deal with the whole mbuf we can move all of the bridging code out of > individual drivers as well. the reason why i _didn't_ do this is performance. In most cases bridges throw away packets so they just need access to the ethernet header. For some cards (e.g. the NE2000) there is a significant advantage in pulling out from the card _only_ the header, and the rest only when the packet is one you really need. The problem is, the ne2000 uses programmed I/O and even on the PCI bus i think the top transfer speed is rather low (could be some 5MB/s or so) meaning that you can only build a full-speed multiport bridge if you do this kind if optimizations _in the driver_ Currently the only driver which uses this optimization is the ne2000 driver. PCI cards using dma master mode probably don't need it at 10mbit/s, and i am not totally sure if it is worthwhile at 100mbit/s where the cost of reprogramming the DMA engine might nuke any advantage. You can argue "get a better card" but i think many people are using picobsd-based bridges (really firewalls) with cheap hardware (plus, here at least ne2000 clones are the only coax cards that i can find). We wouldn't be doing FreeBSD a favour if we removed this optimization. cheers luigi -----------------------------------+------------------------------------- Luigi RIZZO, luigi@iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/ . Universita` di Pisa TEL/FAX: +39-050-568.533/522 . via Diotisalvi 2, 56126 PISA (Italy) http://www.iet.unipi.it/~luigi/ngc99/ ==== First International Workshop on Networked Group Communication ==== -----------------------------------+------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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