netdev - Re: [PATCH net-next] fq_codel: report congestion notification at enqueue time

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Date:	Fri, 29 Jun 2012 07:24:08 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, dave.taht@...il.com,
	codel@...ts.bufferbloat.net, therbert@...gle.com,
	mattmathis@...gle.com, ycheng@...gle.com, nanditad@...gle.com,
	ncardwell@...gle.com
Subject: Re: [PATCH net-next] fq_codel: report congestion notification at
 enqueue time

On Thu, 2012-06-28 at 22:12 -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Fri, 29 Jun 2012 06:53:12 +0200
> 
> > Please dont apply this patch, I'll submit an updated version later.
> 
> Ok.

By the way, I am not sure NET_XMIT_CN is correctly used in RED.

Or maybe my understanding of NET_XMIT_CN is wrong.

If a the packet is dropped in enqueue(), why use NET_XMIT_CN instead of 
NET_XMIT_DROP ?

This seems to mean : I dropped _this_ packet, but dont worry too much, I
might accept other packets, so please go on...

diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c
index 633e32d..0fc5b6c 100644
--- a/net/sched/sch_red.c
+++ b/net/sched/sch_red.c
@@ -77,7 +77,7 @@ static int red_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 		sch->qstats.overlimits++;
 		if (!red_use_ecn(q) || !INET_ECN_set_ce(skb)) {
 			q->stats.prob_drop++;
-			goto congestion_drop;
+			goto drop;
 		}
 
 		q->stats.prob_mark++;
@@ -88,7 +88,7 @@ static int red_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 		if (red_use_harddrop(q) || !red_use_ecn(q) ||
 		    !INET_ECN_set_ce(skb)) {
 			q->stats.forced_drop++;
-			goto congestion_drop;
+			goto drop;
 		}
 
 		q->stats.forced_mark++;
@@ -104,9 +104,8 @@ static int red_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 	}
 	return ret;
 
-congestion_drop:
-	qdisc_drop(skb, sch);
-	return NET_XMIT_CN;
+drop:
+	return qdisc_drop(skb, sch);
 }
 
 static struct sk_buff *red_dequeue(struct Qdisc *sch)


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