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sched: manipulate __QDISC_STATE_RUNNING in qdisc_run_* helpers

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Currently NOLOCK qdiscs pay a measurable overhead to atomically
manipulate the __QDISC_STATE_RUNNING. Such bit is flipped twice per
packet in the uncontended scenario with packet rate below the
line rate: on packed dequeue and on the next, failing dequeue attempt.

This changeset moves the bit manipulation into the qdisc_run_{begin,end}
helpers, so that the bit is now flipped only once per packet, with
measurable performance improvement in the uncontended scenario.

This also allows simplifying the qdisc teardown code path - since
qdisc_is_running() is now effective for each qdisc type - and avoid a
possible race between qdisc_run() and dev_deactivate_many(), as now
the some_qdisc_is_busy() can properly detect NOLOCK qdiscs being busy
dequeuing packets.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni
2018-05-15 10:50:31 +02:00
committed by David S. Miller
parent 5a63f77af7
commit 32f7b44d0f
3 changed files with 19 additions and 24 deletions
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2
net/core/dev.c
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@@ -3244,7 +3244,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
rc = NET_XMIT_DROP;
} else {
rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
__qdisc_run(q);
qdisc_run(q);
}
if (unlikely(to_free))