On Fri, May 14 2021 at 12:44, Alison Chaiken wrote:

On Fri, May 14, 2021 at 11:56 AM Jakub Kicinski [off-list ref] wrote:

quoted

Another thing while I have your attention - ____napi_schedule() does
__raise_softirq_irqoff() which AFAIU does not wake the ksoftirq thread.
On non-RT we get occasional NOHZ warnings when drivers schedule napi
from process context, but on RT this is even more of a problem, right?
ksoftirqd won't run until something else actually wakes it up?

By "NOHZ warnings," do you mean "NOHZ: local_softirq_pending"?    We see
that message about once a week with 4.19.   Presumably any failure of
____napi_schedule() to wake ksoftirqd could only cause problems for the
NET_RX softirq, so if the pending softirq is different, the cause lies
elsewhere.

If you read the above carefully you might notice that this _IS_ about
____napi_schedule() being invoked from task context which raises NET_RX
and then results in pending 08! which is NET_RX.

Thanks,

        tglx