decreasing interrupt CPU load

[Eric Anderson]

Oleg Gawriloff wrote:
> Hello!
> 
> Currently we have router on FreeBSD 4.10-R on SMP 2*PIII 1Ghz. 5sec 
> average traffic trhough fxp on Intel 82550 is about 12kpps (26Mbit/sec). 
> CPU Load on interrupts shown in top and systat -v 1 always above 40%. 
> We've tried to enable polling with HZ=1000, but cpu load does not 
> change, instead round trip time increased from 1ms to 20ms. Also we've 
> tried link0, no success. Is any other options to decrease interrupt cpu 
> load? May be enabling fast forwarding, change fxp to em or bge NIC? Is 
> there exist any drawbacks from enabling fast forwarding?

I've had really great performance with the em NICs, and bad experiences 
with bge's (the hardware is flaky).  You might want to check if the 
interface has checksuming enabled.  I believe disabling/enabling can 
change the performance, however I'm not certain how much, etc.  In 
ifconfig, look for something like:
options=3<rxcsum,txcsum>

If you don't need any firewalling, I would compile a custom kernel with 
as much removed as you can, specifically firewall related items.

Also - it's possible that your bus is the bottleneck - depending on how 
many NICs you have, the type of bus, and the motherboard.

Eric


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Eric Anderson     Sr. Systems Administrator    Centaur Technology
Talk sense to a fool and he calls you foolish.
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