Date: 13 Mar 1999 23:04:29 -0500 From: Cory Kempf <ckempf@enigami.com> To: Bill Paul <wpaul@skynet.ctr.columbia.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: Gigabit ethernet -- what am I doing wrong? Message-ID: <5femmslnsi.fsf@singularity.enigami.com> In-Reply-To: Bill Paul's message of "Fri, 12 Mar 1999 16:16:13 -0500 (EST)" References: <199903122116.QAA19872@skynet.ctr.columbia.edu>
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Nobody else seems to have touched this, so I thought I would toss in my $0.02... Bill Paul <wpaul@skynet.ctr.columbia.edu> writes: > Well, I have my Tigon driver working to the point where I can now exchange > traffic with another machine. But no matter what I do, I can't seem to get > my gigabit ethernet device to generate more than 200Mbps on transmit. I'm > confused. > > Even using jumbo frames, I can't get more than about 200Mbps on transmit. > The LoseNT machine doens't seem to be able to get above 200Mbps either You may well be running in to limitations of the available bandwidth of PCI. The Theoretical Maximum bandwidth is 33MHz * 32 bits = 132 MB/s. That number assumes that you move all the data at once, as a single operation, and your hardware can keep up. Not bloody likely. There is some bus overhead with setting up the data transfer. You can also lose if you are not transfering 32 bit data. If I remember, the worst case was something like 11 or 4MB/s or so. Realistically, on a PowerPC (which is where my experince with PCI is), if you do everything right AND are moving lots of data, you can see up to 96 MB/s. To get this, it is important that the card be able to accept a cache line at a time, and that you deliver a cache line at a time (16 bytes, if memory serves). 200 Mb/s = 25 MB/s, which seems a little low, but is within the realm of what I would expect. Finally, take all this with a grain of salt, as I have never worked with gigabit ethernet... +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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