fq_codel: Avoid regenerating skb flow hash unless necessary

The fq_codel qdisc currently always regenerates the skb flow hash.
This wastes some cycles and prevents flow seperation in cases where
the traffic has been encrypted and can no longer be understood by the
flow dissector.

Change it to use the prexisting flow hash if one exists, and only
regenerate if necessary.

Signed-off-by: Andrew Collins <acollins@cradlepoint.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_fq_codel.c

@@ -57,7 +57,6 @@ struct fq_codel_sched_data {
 	struct fq_codel_flow *flows;	/* Flows table [flows_cnt] */
 	u32		*backlogs;	/* backlog table [flows_cnt] */
 	u32		flows_cnt;	/* number of flows */
-	u32		perturbation;	/* hash perturbation */
 	u32		quantum;	/* psched_mtu(qdisc_dev(sch)); */
 	u32		drop_batch_size;
 	u32		memory_limit;
@@ -75,9 +74,7 @@ struct fq_codel_sched_data {
 static unsigned int fq_codel_hash(const struct fq_codel_sched_data *q,
 				  struct sk_buff *skb)
 {
-	u32 hash = skb_get_hash_perturb(skb, q->perturbation);
-
-	return reciprocal_scale(hash, q->flows_cnt);
+	return reciprocal_scale(skb_get_hash(skb), q->flows_cnt);
 }
 
 static unsigned int fq_codel_classify(struct sk_buff *skb, struct Qdisc *sch,
@@ -482,7 +479,6 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt)
 	q->memory_limit = 32 << 20; /* 32 MBytes */
 	q->drop_batch_size = 64;
 	q->quantum = psched_mtu(qdisc_dev(sch));
-	q->perturbation = prandom_u32();
 	INIT_LIST_HEAD(&q->new_flows);
 	INIT_LIST_HEAD(&q->old_flows);
 	codel_params_init(&q->cparams);