* Eric Dumazet [ref] 2005-07-06 02:32

Hum... shouldnt it be :

+			skb = __qdisc_dequeue_head(qdisc, list + prio);

Correct.

Anyway, the branches misprediction come from the fact that most of packets 
are queued in the prio=2 list.

So each time this function is called, a non unrolled version has to pay 2 
to 5 branches misprediction.

if ((!skb_queue_empty(list + prio))  /* branch not taken, mispredict when 
prio=0 */

The !expr implies an unlikely so the prediction should be right and
equal to your unrolling version.

Maybe we can rewrite the whole thing without branches, examining prio from 
PFIFO_FAST_BANDS-1 down to 0, at least for modern cpu with conditional mov 
(cmov)

This would break the whole thing, the qdisc is supposed to try and
dequeue from the highest priority queue (prio=0) first.