Commit 452f299d authored Jul 18, 2005 by Thomas Graf Committed by David S. Miller Jul 18, 2005

[PKT_SCHED]: Reduce branch mispredictions in pfifo_fast_dequeue



The current call to __qdisc_dequeue_head leads to a branch
misprediction for every loop iteration, the fact that the
most common priority is 2 makes this even worse.  This issue
has been brought up by Eric Dumazet <dada1@cosmosbay.com>
but unlike his solution which was to manually unroll the loop,
this approach preserves the possibility to increase the number
of bands at compile time. 

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent d7c7ed4d

net/sched/sch_generic.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -331,11 +331,10 @@ static struct sk_buff pfifo_fast_dequeue(struct Qdisc qdisc)
		int prio;
		struct sk_buff_head *list = qdisc_priv(qdisc);

		for (prio = 0; prio < PFIFO_FAST_BANDS; prio++, list++) {
		struct sk_buff *skb = __qdisc_dequeue_head(qdisc, list);
		if (skb) {
		for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
		if (!skb_queue_empty(list + prio)) {
		qdisc->q.qlen--;
		return skb;
		return __qdisc_dequeue_head(qdisc, list + prio);
		}
		}