Re: [RFC PATCH 0/4] softirq: Per vector threading v3

Dmitry Safonov
2018-01-23T12:32:19Z

On Tue, 2018-01-23 at 11:13 +0100, Paolo Abeni wrote:
> Hi,
>
> On Fri, 2018-01-19 at 16:46 +0100, Frederic Weisbecker wrote:
> > As per Linus suggestion, this take doesn't limit the number of
> > occurences
> > per jiffy anymore but instead defers a vector to workqueues as soon
> > as
> > it gets re-enqueued on IRQ tail.
> >
> > No tunable here, so testing should be easier.
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-
> > dynticks.git
> > softirq/thread-v3
> >
> > HEAD: 6835e92cbd70ef4a056987d2e1ed383b294429d4
>
> I tested this series in the UDP flood scenario, binding the user
> space
> process receiving the packets on the same CPU processing the related
> IRQ, and the tput sinks nearly to 0, like before Eric's patch.
>
> The perf tool says that almost all the softirq processing is done
> inside the workqueue, but the user space process is scheduled very
> rarely, while before this series, in this scenario, ksoftirqd and the
> user space process got a fair share of the CPU time.

It get a fair share of the CPU time only on some lucky platforms (maybe
on the most). On other not-so-lucky platforms it was also unfair - as
I've previously described by the reason of slow raising softirqs :-/

--
Thanks,
Dmitry