[asterisk-users] Re: Balancing interrupts.

[Daniel Pittman]

Steve Edwards <asterisk.org at sedwards.com> writes:

> I see the following on one of my new servers:
>
> -ts10::sedwards:~$ cat /proc/interrupts
>             CPU0       CPU1       CPU2       CPU3
>    0:    2979045    2988620   87780075   87779501    IO-APIC-edge  timer

[...]

> 225:    4611916     681023   84732445   89903138   IO-APIC-level  wct4xxp
> NMI:          0          0          0          0
> LOC:  181534588  181534654  181534653  181534652
> ERR:          0
> MIS:          0
>
> -ts10::sedwards:~$ ps -e | grep bal
>   2633 ?        00:00:00 irqbalance
>
> Should I be concerned that cpu1 is servicing only 700,000 interrupts
> from my te410p while cpu3 is servicing almost 90,000,000?
>
> I thought this is what irqbalance was for...

Actually, what you *really* want (for performance reasons) is to have
one CPU handle *all* the interrupts and all the threads that talk to
hardware for that card, if possible.

Every time you move the IRQ to a different CPU you lose a bunch of
cycles reloading data from main memory into the L2 and L1 cache, cycles
that can't be used elsewhere.

Binding that interrupt to one specific CPU -- and your NIC to a
different CPU -- is generally a good idea.  If you can keep the threads
that handle those signals and the hardware on that same CPU you increase
efficiency a bit more.

Moving the IRQ has plenty of cost and isn't a great plan.  :)

Regards,
        Daniel
-- 
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