pf performance?

[Erich Weiler]

>> 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.

Ah, I see.  Definitely appears for me in interrupts then.  I've got the 
mxge driver doing the work here.  So, given that I can spread out the 
interrupts to every core (like, pin an interrupt queue to each core), I 
can have all my cores work on the process.  But seeing as though the pf 
bit is still serialized I'm not sure that I understand how it is 
serialized when many CPUs are handling interrupts, and hence doing the 
work of pf as well?  Wouldn't that indicate that the work of pf is being 
handled by many cores, as many cores are handling the interrupts?

Or are you saying that pf *is* being handled by many cores, but just in 
a serialized nature?  Like, packet 1 is handled by core 0, then packet 2 
is handled by core 1, packet 3 is handled by core 4, etc?  Such that 
even though multiple cores are handling it, they are just doing so 
serially and not in parallel?  And if so, maybe it still helps to have 
many cores?

Thanks for all the excellent info!

>> 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.
>