Re: RFC: softint-based if_input

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

Hi Joerg,

Thanks for your comment!

On Fri, Jan 15, 2016 at 6:43 AM, Joerg Sonnenberger
<joerg%britannica.bec.de@localhost> wrote:
> On Thu, Jan 14, 2016 at 07:19:03PM +0900, Ryota Ozaki wrote:
>> One possible objection should be performance
>> degradation, however I believe we can mitigate
>> by introducing polling packet processing
>> like Linux and FreeBSD do. Of course, we also
>> have to rethink existing sofint (L3 softints
>> and bridge_forward softint).
>
> While I agree with the goal and also that fast-forward shouldn't stop
> this, I would like to see some numbers for the performance impact under
> load and maybe the latency change without load. Any chance to test for
> that?

I'm preparing performance numbers. They'll come early
in the next week.

>
>> BTW, this proposal includes another change;
>> move bpf_mtap to a common place, not doing it
>> in each driver. This change is also needed by
>> the above proposal to ensure to always run bpf
>> in softint.
>
> Be careful, there are multiple BPF hooks in some drivers, e.g. the
> WiFi stack.

Hmm. Okay, I'll check all hooks...


BTW, I forgot noting that ipi_sysinit in main() needed a tweak
to use pktq_create in driver attach routines. The tweak is
like this finally:
http://www.netbsd.org/~ozaki-r/fix-ipi_sysinit.diff

pktq_create calls softint_establish with SOFTINT_RCPU and
then softint_establish calls ipi_register which depends
on ipi_sysinit is finished. However, driver attach routines
are called in configure() in main() that is prior to
ipi_sysinit. So I need to move ipi_sysinit to a place
before configure(). Unfortunately, the original ipi_sysinit
depends on ncpu that is determined after configure() so
I have to divide ipi_sysinit into two: one is for
softint_establish and moved to a place before configure(),
and the other depending on ncpu is kept at the original place.

I confirmed it works on amd64, but I'm not sure the change
doesn't break other archs. Could someone expert on IPI check it?

Thanks,
  ozaki-r