Re: [PATCH] NUMA-Q disable irqbalance

["Martin J. Bligh" <Martin.Bligh@us.ibm.com>]

>> On a collection of networking workloads the P4 is about 5% better
>> performing with the irq balancer off.
> 
> Hmm. And I could _feel_ how my dual HT P4 was slow before the irq issues 
> were fixed.
> 
> Now, there have been other changes too - like the scheduler (and my
> current P4 has a different SCSI interface), but I dunno. The thing I 
> attributed the improvements in interactive feel was the fact that the work 
> got balanced out more sanely.

Was that before or after you changed HZ to 1000? I *think* that increased
the frequency of IO-APIC reprogramming by a factor of 10, though I might
be misreading the code. If it does depend on HZ, I think that's bad.

People in our benchmarking group (Andrew, cc'ed) have told me that 
reducing the frequency of IO-APIC reprogramming by a factor of 20 or so
improves performance greatly  - don't know what HZ that was at, but the
whole thing seems a little overenthusiastic to me.

M.