Date: Sun, 14 Mar 1999 05:44:28 -0600 From: "Rob Snow" <rsnow@lgc.com> To: "Amancio Hasty" <hasty@rah.star-gate.com>, "Cory Kempf" <ckempf@enigami.com> Cc: "Bill Paul" <wpaul@skynet.ctr.columbia.edu>, <freebsd-hackers@FreeBSD.ORG> Subject: Re: Gigabit ethernet -- what am I doing wrong? Message-ID: <001b01be6e10$08061120$03e48486@dympna.com>
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I'm looking at this wondering a couple of things. How many mem copies take place in the IP stack before we're ready to transmit a frame? My question is based around whether it's the NIC's or the IP stacks and PCI holding us back. What would PCI-64@66 do for us with current stacks? -Rob ----- Original Message ----- From: Cory Kempf <ckempf@enigami.com> To: Amancio Hasty <hasty@rah.star-gate.com> Cc: Bill Paul <wpaul@skynet.ctr.columbia.edu>; <freebsd-hackers@FreeBSD.ORG> Sent: Saturday, March 13, 1999 11:22 PM Subject: Re: Gigabit ethernet -- what am I doing wrong? >Amancio Hasty <hasty@rah.star-gate.com> writes: > >> > 200 Mb/s = 25 MB/s, which seems a little low, but is within the realm of >> > what I would expect. >> >> I think the system should be able to support at least 70MB/s at least I >> do over here >> with a bt848 video capture board capturing 640x480x4 at 30 frames per second >> and then displaying the frames on video display card 8) > >A video capture board is generally moving bulk data without any protocol >in the way. It is idealy suited for getting maximal bandwidth from PCI, >as you can essentially set up the transfer, then just let it run. > >With an ethernet driver, though, there is often additional host<->card >traffic, such as telling the card "here is some data", the card responding >"Ok, I am done with it", etc. Additionally, the protocol doesn't lend >itself to exclusively bulk data transfers. ARP and other overhead will >eat up a lot of that theoretical bandwidth. > >So, if you are seeing 70 MB/s with video, where you can probably get by >with a single ACK between frames -- i.e. 2 bus operations / block -- it >wouldn't surprise me to see an ethernet card, with a protocol that might >require five bus operations / block getting less. > >Remember too, that trip through the protocol stack was only a little >over 50 MB/s... > >+C > >-- >Thinking of purchasing RAM from the Chip Merchant? >Please read this first: <http://www.enigami.com/~ckempf/chipmerchant.html>; > >Cory Kempf Macintosh / Unix Consulting & Software Development >ckempf@enigami.com <http://www.enigami.com/~ckempf/>; > > >To Unsubscribe: send mail to majordomo@FreeBSD.org >with "unsubscribe freebsd-hackers" in the body of the message > > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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