fq_codel: should use qdisc backlog as threshold

codel_should_drop() logic allows a packet being not dropped if queue
size is under max packet size.

In fq_codel, we have two possible backlogs : The qdisc global one, and
the flow local one.

The meaningful one for codel_should_drop() should be the global backlog,
not the per flow one, so that thin flows can have a non zero drop/mark
probability.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Dave Taht <dave.taht@bufferbloat.net>
Cc: Kathleen Nichols <nichols@pollere.com>
Cc: Van Jacobson <van@pollere.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_codel.c

@@ -77,8 +77,8 @@ static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch)
 	struct codel_sched_data *q = qdisc_priv(sch);
 	struct sk_buff *skb;
 
-	skb = codel_dequeue(sch, &q->params, &q->vars, &q->stats,
-			    dequeue, &sch->qstats.backlog);
+	skb = codel_dequeue(sch, &q->params, &q->vars, &q->stats, dequeue);
+
 	/* We cant call qdisc_tree_decrease_qlen() if our qlen is 0,
 	 * or HTB crashes. Defer it for next round.
 	 */

net/sched/sch_fq_codel.c

@@ -217,13 +217,14 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
  */
 static struct sk_buff *dequeue(struct codel_vars *vars, struct Qdisc *sch)
 {
+	struct fq_codel_sched_data *q = qdisc_priv(sch);
 	struct fq_codel_flow *flow;
 	struct sk_buff *skb = NULL;
 
 	flow = container_of(vars, struct fq_codel_flow, cvars);
 	if (flow->head) {
 		skb = dequeue_head(flow);
-		sch->qstats.backlog -= qdisc_pkt_len(skb);
+		q->backlogs[flow - q->flows] -= qdisc_pkt_len(skb);
 		sch->q.qlen--;
 	}
 	return skb;
@@ -256,7 +257,7 @@ begin:
 	prev_ecn_mark = q->cstats.ecn_mark;
 
 	skb = codel_dequeue(sch, &q->cparams, &flow->cvars, &q->cstats,
-			    dequeue, &q->backlogs[flow - q->flows]);
+			    dequeue);
 
 	flow->dropped += q->cstats.drop_count - prev_drop_count;
 	flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;