Subject: [RFC PATCH] sched: Fix resource limiting in pfifo_fast

From: Krishna Kumar <[email-masked]>
Date: Sun, 30 Aug 2009 11:53:44 +0530

From: Krishna Kumar <[email-masked]>

pfifo_fast_enqueue has this check:
        if (skb_queue_len(list) < qdisc_dev(qdisc)->tx_queue_len) {

which allows each band to enqueue upto tx_queue_len skbs for a
total of 3*tx_queue_len skbs. I am not sure if this was the
intention of limiting in qdisc.

Patch compiled and 32 simultaneous netperf testing ran fine. Also:
# tc -s qdisc show dev eth2
qdisc pfifo_fast 0: root bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
 Sent 16835026752 bytes 373116 pkt (dropped 0, overlimits 0 requeues 25) 
 rate 0bit 0pps backlog 0b 0p requeues 25 

(I am taking next week off, so sorry for any delay in responding)

Signed-off-by: Krishna Kumar <[email-masked]>
---

 net/sched/sch_generic.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff -ruNp org/net/sched/sch_generic.c new/net/sched/sch_generic.c
--- org/net/sched/sch_generic.c	2009-08-30 11:18:23.000000000 +0530
+++ new/net/sched/sch_generic.c	2009-08-30 11:21:50.000000000 +0530
@@ -432,11 +432,11 @@ static inline struct sk_buff_head *band2
 
 static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc* qdisc)
 {
-	int band = prio2band[skb->priority & TC_PRIO_MAX];
-	struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
-	struct sk_buff_head *list = band2list(priv, band);
+	if (skb_queue_len(&qdisc->q) < qdisc_dev(qdisc)->tx_queue_len) {
+		int band = prio2band[skb->priority & TC_PRIO_MAX];
+		struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
+		struct sk_buff_head *list = band2list(priv, band);
 
-	if (skb_queue_len(list) < qdisc_dev(qdisc)->tx_queue_len) {
 		priv->bitmap |= (1 << band);
 		qdisc->q.qlen++;
 		return __qdisc_enqueue_tail(skb, qdisc, list);