Ted Mittelstaedt wrote, On 12/13/2005 12:44 AM:
-----Original Message-----
From: Drew Tomlinson [mailto:[EMAIL PROTECTED]
Sent: Monday, December 12, 2005 12:30 PM
To: Ted Mittelstaedt
Cc: Michael Vince; [EMAIL PROTECTED]; [email protected];
Kris Kennaway
Subject: Polling For 100 mbps Connections? (Was Re: Freebsd Theme Song)
On 12/12/2005 8:13 AM Ted Mittelstaedt wrote:
Michael,
Fundamentally, here's the problem Danial is claiming exists:
it takes a certain amount of time to get the packet clocked in
from the network into the ethernet receiver. This is hardware
dependent and cannot be changed.
It takes a certain amount of time to get the packet out of
the hardware in the ethernet card into main ram, this also
hardware dependent and cannot be changed. (unless the device
driver is terribly inefficient, which we will assume it's not)
Once in main ram, the information in the packet has to go through
a number of code statements. The more code statements the
longer the information in the packet is sitting around in
the FreeBSD system's memory.
It then takes a certain amount of time to get the information
out of main memory into the other sending ethernet nic's buffers,
and it takes time to get it out of the sending nic back to the
wire.
Danial is claiming the slowness is in the main ram section of
things, not in the ethernet driver code.
polling makes the ethernet driver more efficient at high data
rates, but it does nothing for the speed of processing within
the TCPIP stack itself. At low data rates polling is less
efficient than the interrupt method. And unless the nic driver
is terribly inefficient to start with, the time it adds to the
packet path in the system is minor compared to the time spent
in the TCP/IP stack.
Ted
Thanks for the explanation. So would polling be beneficial or
detrimental for a 100 mbps Ethernet card?
Yes, if you were running 100Mbt's of bandwidth through it.
I assume you mean "yes it's beneficial"? :)
Not sure if 100 mbps is
considered "high" or "low" speed. I'm specifically interested in
NetGear cards using the dc driver or DLink cards using the rl driver.
The rl chipset isn't known as a very good chipset. YMMV
Yeah, I've heard that a lot. It was an old card I had lying around and
it seems to work OK for me. I'm not using it for anything other that
connecting to a 802.11b wireless bridge. Very little traffic.
Some of the Netgear cards use clone 21143 chipsets which are
extremely inferior to the real thing. In particular if your
Netgear card is using a PNIC chipset it is pretty bad with serious
performance penalty. This is documented in Section 4 of the dc manpage.
This is disapointing. I was under the impression that NetGear cards
were pretty good. But now I looked closer at dmesg.boot and see I have
the PNIC chipset you mention. I'll read the dc man page to see what
penalties I'm suffering.
People seem to have good results with polling on the fxp cards.
Ah, the built in interface on a HP e60 server I have. It's an old dog
used as a file server. It has been nothing but reliable and is still
chuggin' along just fine. I'll enable polling on it and see if there's
any noticeable improvement in transfer rates. The machine that
typically is used for large file transfers to and from the e60 is a
Windows XP box that has a Nvidia Nforce 4 chipset and whatever
intergrated ethernet port that comes with that chipset. Are there any
known issues with this setup that would invalidate my test?
Thanks again for the info.
Drew
Ted
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