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    SubjectRe: [PATCH 3/3] softirq: don't yield if only expedited handlers are pending
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    Jakub!

    On Thu, Dec 22 2022 at 14:12, Jakub Kicinski wrote:
    > This leads to a situation where we go thru the softirq loop twice.
    > First round we have pending = NET (from the NIC IRQ/NAPI), and
    > the second iteration has pending = TASKLET (the socket tasklet).

    ...

    > diff --git a/kernel/softirq.c b/kernel/softirq.c
    > index ad200d386ec1..4ac59ffb0d55 100644
    > --- a/kernel/softirq.c
    > +++ b/kernel/softirq.c
    > @@ -601,7 +601,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
    >
    > if (time_is_before_eq_jiffies(end) || !--max_restart)
    > limit = SOFTIRQ_OVERLOAD_TIME;
    > - else if (need_resched())
    > + else if (need_resched() && pending & ~SOFTIRQ_NOW_MASK)
    > limit = SOFTIRQ_DEFER_TIME;
    > else
    > goto restart;

    While this is the least of my softirq worries on PREEMPT_RT, Peter is
    right about real-time tasks being deferred on a PREEMPT_RT=n
    kernel. That's a real issue for low-latency audio which John Stultz is
    trying to resolve. Especially as the above check can go in circles.

    I fear we need to go back to the drawing board and come up with a real
    solution which takes these contradicting aspects into account. Let me
    stare at Peters and Johns patches for a while.

    Thanks

    tglx


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