[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>
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 73e218e..8edefd5d 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -331,11 +331,10 @@
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);
}
}