pf performance?

["Clément Hermann (nodens)"]

Hi,

this thread seems it seems to be related to my problem (see High CPU 
interrupt load on intekl i350T4 with igb on 8.3). So let me jump in ;)

Le 26/04/2013 17:54, Andre Oppermann a écrit :
> On 26.04.2013 16:49, Erich Weiler wrote:
>>> The pf isn't a process, so you can't see it in top. pf has some helper
>>> threads however, but packet processing isn't performed by any of them.
>>
>> But the work pf does would show up in 'system' on top right?  So if I 
>> see all my CPUs tied up 100%
>> in 'interrupts' and very little 'system', would it be a reasonable 
>> assumption to think that if I got
>> more CPU cores to handle the interrupts that eventually I would see 
>> 'system' load increase as the
>> interrupt load became faster to be handled?  And thus increase my 
>> bandwidth?
>
> Having the work of pf show up in 'interrupts' or 'system' depends on the
> network driver and how it handles sending packets up the stack. In most
> cases drivers deliver packets from interrupt context.
>
That is very interesting. Do you think my High CPU interrupt problem 
could be related to the fact that we use pf + altq ?

>> In other words, until I see like 100% system usage in one core, I 
>> would have room to grow?
>
> You have room to grow if 'idle' is more than 0% and the interrupts of
> the networks cards are running on different cores.  If one core gets
> all the interrupts a second idle core doesn't get the chance to help
> out.  IIRC the interrupt allocation to cores is done at interrupt
> registration time or driver attach time.  It can be re-distributed
> at run time on most architecture but I'm not sure we have an easily
> accessible API for that.
>
Would it be possible to use cpu affinity to reserve a core to pf ? For 
instance, use only 7 queues per card and keep a core available to pf ? 
Does that make sense or would the pf lock impact the interrupts of the 
interface queues ? I see a lot of "WAIT" state on the queues when I do a 
top -CHSIz.


Cheers,

-- 
Clément (nodens)