FreeBSD 5.4 network performance with SMP

Robert Lindgren robert at
Sun Oct 2 13:09:46 PDT 2005

Hi All,

I have a strange little problem on Dell 1800's. If HT,SMP is enabled in the 
kernel (5.4p7), performance on the integrated em0 is not especially good, 
half the speed of the current 100Mbit connection. This is true from the 
server and a little better to  the server. On a pci rl0 card in the same 
machine performance is even worse. About 15Mbit from the server!

Then I read a lot of people having poor performance from the rl0 cards and a 
lot of FreeBSD people bashing it for being crap, even in the source code for 
the module it's stated that these cards aren't so good. I guess that is right 
to some extent but not 15Mbit/sec.

So when I rebuilt the kernel without HT and SMP I get full wirespeed from the 
em0 and the rl0 (100Mbit/sec). Is there anything I've been doing wrong to get 
hit by this poor performance with the SMP kernel. I read the disabling USB 
could improve performance but tried that with the HT kernel without any luck.

The server has 1 3Ghz cpu, and I would prefer too run a HT enabled kernel, but 
not with that kind of performance, so please advice. The same machines (Dell 
1800) run linux with HT enabled without any network performance degradation.

Best regards
Robert Lindgren

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