[TriLUG] hyperthreading, smp, and irqbalance

[Greg Cox]

> I have a production file server (P4 2.8ghz w/HT), that is approaching
> its quarterly scheduled maintenance downtime.  I'm wondering if it's
> worth switching to an SMP kernel to take advantage of hyperthreading.
>
> The box runs very happily on its current 2.6.8-3 Debian Sarge kernel.
>
> Are there any risks to SMP on a single CPU w/HT?

We have a postgres box, 2 hyperthreaded singlecore processors (so 4
procs to what Linux sees).  We have performance problems with it
sometimes, spending a lot of time in iowait.  Our current THEORY
(add salt here) is that it's swapping postmaster processes around
the HTs as if they were real processors, but blocking because they
aren't.

It's just a theory, and that's the only case where we're suspicious it's
a problem.