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SubjectLinux switching [Was: network nicety]
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On 11-Oct-98 Gregory Maxwell wrote:
> What is Linux's current briding performance like?

If you're comparing with a commercial ethernet switch, pretty poor. At least
the 3Coms start transmitting the packet to the destination as soon as they
have recieved the Ethernet frame containing the destination address,[1]
whereas Linux waits until the entire packet has been received. On 1500 byte
packets at 100Mbs, the former gives a latency of 8x20x10ns = 1.6us, whereas
the latter is about 8x1526x10ns = ~122us. (Assuming the Linux box starts
transmitting the moment it recieves the packet, which it won't) I'd *guess*
you'd see network performance improve only if your existing network regularly
runs above 80% utilisation, which is pretty extreme. Ethernet switches aren't
that expensive these days anyway.

On the card front, Tulip seems to be the preferred card for Linux ATM. I've
use 3Com recently without major problems, although it won't fast-swtich and
I understand the 3C905B has problems w.r.t. Linux. Similar story for Intel
cards.

[1] Using, for example, fast-switch mode on the 1000/3000. The Fragment-Free/
Store and forward option disappeared on the 1100/3300, I guess it's automatic
now but I don't know for sure.

Ryan O'Connell - http://mipc-01.brunel.ac.uk:8080/
<nemesis@eh.org> -- <cs95rro@brunel.ac.uk>


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