User process starvation in FreeBSD 5.3

[Stefan Bethke]

Am 03.01.2005 um 23:23 schrieb Youlin Feng:

> We are building a network appliance running FreeBSD 5.3 and under very
> heavy network traffic the user processes don't get scheduled for an
> unacceptable period of time. Marking the user process/thread real-time
> class doesn't help since the real-time user threads priorities are 
> still
> lower than the interrupt threads.

The effect you're describing very much sounds like 'livelock': the 
system is so overwhelmed with interrupts that it has no time to do 
anything else but servicing them. FreeBSD offers polling(4), which is 
intended to mitigate the overhead of a high interrupt rate on certain 
network controllers; especially in high-throughput scenarios, it can 
improve system load, throughput, and latency quite dramatically.

On the other hand, your hardware might just not be able handle the 
packet rate.

I'd suggest asking this on freebsd-net, where I believe quite a few 
people with experience in high-throughput setups are reading.


Cheers,
Stefan

-- 
Stefan Bethke <stb at lassitu.de>   Fon +49 170 346 0140