Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd context

[Frederic Weisbecker]

On Wed, Jan 10, 2018 at 08:19:49PM -0800, Linus Torvalds wrote:
> On Wed, Jan 10, 2018 at 7:22 PM, Frederic Weisbecker
> <frederic@xxxxxxxxxx> wrote:
> >
> > Makes sense, but I think you need to keep the TASK_RUNNING check.
> 
> Yes, good point.
> 
> > So perhaps it should be:
> >
> > -       return tsk && (tsk->state == TASK_RUNNING);
> > +       return (tsk == current) && (tsk->state == TASK_RUNNING);
> 
> Looks good to me - definitely worth trying.
> 
> Maybe that weakens the thing so much that it doesn't actually help the
> UDP packet storm case?
> 
> And maybe it's not sufficient for the dvb issue.
> 
> But I think it's worth at least testing. Maybe it makes neither side
> entirely happy, but maybe it might be a good halfway point?

Yes I believe Dmitry is facing a different problem where he would rather
see ksoftirqd scheduled more often to handle the queue as a deferred batch
instead of having it served one by one on the tails of IRQ storms.
(Dmitry correct me if I misunderstood).

But your patch still seems to make sense for the case you described: when
ksoftirqd is voluntarily preempted off and the current IRQ could handle the
queue.