Date: 14 Mar 1999 00:22:37 -0500 From: Cory Kempf <ckempf@enigami.com> To: Amancio Hasty <hasty@rah.star-gate.com> Subject: Re: Gigabit ethernet -- what am I doing wrong? Message-ID: <5fd82clk6a.fsf@singularity.enigami.com> In-Reply-To: Amancio Hasty's message of "Sat, 13 Mar 1999 21:00:24 -0800" References: <199903140500.VAA73230@rah.star-gate.com>
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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
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