On Fri, Dec 03, 2004 at 11:36:08PM +0200, Mihai CHELARU wrote:
> Hello Thor,
> 
> Thor Lancelot Simon wrote:
> >On Fri, Dec 03, 2004 at 11:02:22AM +0200, Mihai CHELARU wrote:
> >
> >>Software tweaks:
> >>	- HZ 1000
> >>
> >>So, I have 4000 IRQs/sec generated by scheduler. Rest of IRQs/sec is 
> >
> >
> >I'm a little confused by this.  If you've set HZ=1000 (which is a very
> >bad thing to set it to; the table for doing quick time computations based
> >on HZ has an entry for 1024, but not for 1000), why are you getting *4000*
> >interrupts per second?
> >
> 
> 2 CPUs and hyperthreading. This is what `systat vmstat 1` is reporting 
> me. 1000 irqs/sec for each of the for CPUs. So a total of 4000 IRQs/sec. 
> Good to know about that quick time computations table at 1024, I'll 
> modify ASAP.

Hm.  Maybe 3000 of those IRQs are timer update IPIs (though I don't
_think_ that's how it's supposed to work).

Are you sure you really want hyperthreading switched on?  With two
physical CPUs, our scheduler may not give you the best performance
with them set up that way.  You should test and see (with a single
physical CPU, hyperthreading is in fact usually a win, but a very
slight one).

Also, do you really need such a high value of HZ?  You might find that
decreasing HZ to 256 or 512 gave you a useful reduction in interrupt
load with little downside.