From owner-freebsd-hackers Sat Mar 13 21:50:10 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from rah.star-gate.com (rah.star-gate.com [209.249.129.138]) by hub.freebsd.org (Postfix) with ESMTP id DEF2514FBB for ; Sat, 13 Mar 1999 21:49:46 -0800 (PST) (envelope-from hasty@rah.star-gate.com) Received: from rah.star-gate.com (localhost.star-gate.com [127.0.0.1]) by rah.star-gate.com (8.9.1/8.8.8) with ESMTP id VAA74949; Sat, 13 Mar 1999 21:48:47 -0800 (PST) (envelope-from hasty@rah.star-gate.com) Message-Id: <199903140548.VAA74949@rah.star-gate.com> X-Mailer: exmh version 2.0.2 2/24/98 To: Cory Kempf Cc: Bill Paul , freebsd-hackers@FreeBSD.ORG Subject: Re: Gigabit ethernet -- what am I doing wrong? In-reply-to: Your message of "14 Mar 1999 00:22:37 EST." <5fd82clk6a.fsf@singularity.enigami.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Sat, 13 Mar 1999 21:48:47 -0800 From: Amancio Hasty Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Point well taken , however in the case of the bt848 driver there is a protocol between the host and the card in the form of a dma controller program which tells programs the bt848's dma controller so in reality there two data streams : host -- program ( line 1. to memory region line 2. to memory region line 3. to memory region ) it is a bit more involved than that however that is the essence of it. And you are correct there are FreeBSD systems out there which do saturate the PCI bus with bt848 cards . Not too long ago above.net was testing a security cam setup using 3 bt848s and transmitting the data to the mbone using FreeBSD of course 8) Have Fun Guys, Amancio > Amancio Hasty 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: > > Cory Kempf Macintosh / Unix Consulting & Software Development > ckempf@enigami.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message