[TriLUG] hyperthreading, smp, and irqbalance

[Kevin Flanagan]

Dane,

Turning on HT would depend, are you CPU bound?  If so, and you aren't IO 
bound then it may be a good move. 



Greg,

Can you fiddle with processor affinity?  I don't know if any of the 
distros support that.  If you can force your postmaster process to stick 
to one CPU, and let the kernel manage the other processes as it sees fit.




Kevin


Greg Cox wrote:
>> 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.