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    SubjectRe: [PATCH net-next 2/2] net: exit busy loop when another process is runnable
    On Fri, Aug 22, 2014 at 07:01:05AM +0200, Mike Galbraith wrote:
    > > +++ b/include/net/busy_poll.h
    > > @@ -109,7 +109,8 @@ static inline bool sk_busy_loop(struct sock *sk, int nonblock)
    > > cpu_relax();
    > >
    > > } while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) &&
    > > - !need_resched() && !busy_loop_timeout(end_time));
    > > + !need_resched() && !busy_loop_timeout(end_time) &&
    > > + nr_running_this_cpu() < 2);
    > >

    So as has been said by now; this is horrible.

    We should not export nr_running like this ever. Your usage of < 2
    implies this can be hit with nr_running == 0, and therefore you can also
    hit it with nr_running == 1 where the one is not network related and you
    get random delays.

    Worse still, you have BH (and thereby preemption) disabled, you should
    not _ever_ have undefined and indefinite waits like that.

    You also destroy any hope of dropping into lower power states; even when
    there's never going to be a packet ever again, also bad.

    All in all, a complete trainwreck.

    NAK.


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