Date: Sat, 13 Mar 1999 21:48:47 -0800 From: Amancio Hasty <hasty@rah.star-gate.com> To: 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: <199903140548.VAA74949@rah.star-gate.com> In-Reply-To: Your message of "14 Mar 1999 00:22:37 EST." <5fd82clk6a.fsf@singularity.enigami.com>
next in thread | previous in thread | raw e-mail | index | archive | help
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 <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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199903140548.VAA74949>