[Codel] [RFC PATCH] Codel: Enable packet drop with ECN-marked packets on a threshold

[Dave Täht]

Lossless IP networks are not possible. Dropping packets is the
fastest way to get back to a target delay, and if that involves
dropping ECN marked packets, so be it. When a network is in a
more steady state, ECN is fine...

My choice of "2 * target" as a threshold for dropping ECN
marked packets is entirely arbitrary.
---
 include/net/codel.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/net/codel.h b/include/net/codel.h
index 550debf..26944a0 100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -280,7 +280,8 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
 						* since there is no more divide
 						*/
 				codel_Newton_step(vars);
-				if (params->ecn && INET_ECN_set_ce(skb)) {
+				if (params->ecn && INET_ECN_set_ce(skb) &&
+					vars->ldelay <= 2 * params->target) {
 					stats->ecn_mark++;
 					vars->drop_next =
 						codel_control_law(vars->drop_next,
@@ -305,7 +306,8 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
 			}
 		}
 	} else if (drop) {
-		if (params->ecn && INET_ECN_set_ce(skb)) {
+		if (params->ecn && INET_ECN_set_ce(skb) &&
+		        vars->ldelay <= 2 * params->target) {
 			stats->ecn_mark++;
 		} else {
 			qdisc_drop(skb, sch);
-- 
1.7.9.5