[Codel] [RFCv2 PATCH] codel: add ecn_target for when to drop rather than mark ecn packets

["Dave Täht" <dave.taht@bufferbloat.net>]

From: Dave Taht <dave.taht@bufferbloat.net>

ECN can be gamed, and it is generally faster under overload
to drop rather than mark packets, to get back to a target.

This patch adds support for ecn_target which controls when
codel and fq_codel will start dropping rather than marking
ecn tagged packets.

The default is 15ms.
---
 include/linux/pkt_sched.h |    2 ++
 include/net/codel.h       |   11 +++++++++--
 net/sched/sch_codel.c     |   13 ++++++++++++-
 net/sched/sch_fq_codel.c  |   12 +++++++++++-
 4 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index 32aef0a..f0dcf8c 100644
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -663,6 +663,7 @@ enum {
 	TCA_CODEL_LIMIT,
 	TCA_CODEL_INTERVAL,
 	TCA_CODEL_ECN,
+	TCA_CODEL_ECN_TARGET,
 	__TCA_CODEL_MAX
 };
 
@@ -691,6 +692,7 @@ enum {
 	TCA_FQ_CODEL_ECN,
 	TCA_FQ_CODEL_FLOWS,
 	TCA_FQ_CODEL_QUANTUM,
+	TCA_FQ_CODEL_ECN_TARGET,
 	__TCA_FQ_CODEL_MAX
 };
 
diff --git a/include/net/codel.h b/include/net/codel.h
index 550debf..8a6a2b0 100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -111,11 +111,13 @@ static inline u32 codel_time_to_us(codel_time_t val)
  * @target:	target queue size (in time units)
  * @interval:	width of moving time window
  * @ecn:	is Explicit Congestion Notification enabled
+ * @ecn_target:	ecn target for queue drop anyway (in time units)
  */
 struct codel_params {
 	codel_time_t	target;
 	codel_time_t	interval;
 	bool		ecn;
+	codel_time_t	ecn_target;
 };
 
 /**
@@ -161,6 +163,7 @@ static void codel_params_init(struct codel_params *params)
 	params->interval = MS2TIME(100);
 	params->target = MS2TIME(5);
 	params->ecn = false;
+	params->ecn_target = MS2TIME(15);
 }
 
 static void codel_vars_init(struct codel_vars *vars)
@@ -280,7 +283,9 @@ 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 && 
+				    params->ecn_target > vars->ldelay &&
+					INET_ECN_set_ce(skb)) {
 					stats->ecn_mark++;
 					vars->drop_next =
 						codel_control_law(vars->drop_next,
@@ -305,7 +310,9 @@ static struct sk_buff *codel_dequeue(struct Qdisc *sch,
 			}
 		}
 	} else if (drop) {
-		if (params->ecn && INET_ECN_set_ce(skb)) {
+		if (params->ecn && 
+		    params->ecn_target > vars->ldelay &&
+		    INET_ECN_set_ce(skb)) {
 			stats->ecn_mark++;
 		} else {
 			qdisc_drop(skb, sch);
diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
index 2f9ab17..b008a35 100644
--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -109,6 +109,7 @@ static const struct nla_policy codel_policy[TCA_CODEL_MAX + 1] = {
 	[TCA_CODEL_LIMIT]	= { .type = NLA_U32 },
 	[TCA_CODEL_INTERVAL]	= { .type = NLA_U32 },
 	[TCA_CODEL_ECN]		= { .type = NLA_U32 },
+	[TCA_CODEL_ECN_TARGET]	= { .type = NLA_U32 },
 };
 
 static int codel_change(struct Qdisc *sch, struct nlattr *opt)
@@ -133,6 +134,13 @@ static int codel_change(struct Qdisc *sch, struct nlattr *opt)
 		q->params.target = ((u64)target * NSEC_PER_USEC) >> CODEL_SHIFT;
 	}
 
+	if (tb[TCA_CODEL_ECN_TARGET]) {
+		u32 target = nla_get_u32(tb[TCA_CODEL_TARGET]);
+
+		q->params.ecn_target = ((u64)target * NSEC_PER_USEC) >> 
+				 	CODEL_SHIFT;
+	}
+
 	if (tb[TCA_CODEL_INTERVAL]) {
 		u32 interval = nla_get_u32(tb[TCA_CODEL_INTERVAL]);
 
@@ -145,6 +153,7 @@ static int codel_change(struct Qdisc *sch, struct nlattr *opt)
 	if (tb[TCA_CODEL_ECN])
 		q->params.ecn = !!nla_get_u32(tb[TCA_CODEL_ECN]);
 
+
 	qlen = sch->q.qlen;
 	while (sch->q.qlen > sch->limit) {
 		struct sk_buff *skb = __skb_dequeue(&sch->q);
@@ -199,7 +208,9 @@ static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
 	    nla_put_u32(skb, TCA_CODEL_INTERVAL,
 			codel_time_to_us(q->params.interval)) ||
 	    nla_put_u32(skb, TCA_CODEL_ECN,
-			q->params.ecn))
+			q->params.ecn) ||
+	    nla_put_u32(skb, TCA_CODEL_ECN_TARGET,
+			codel_time_to_us(q->params.ecn_target)))
 		goto nla_put_failure;
 
 	return nla_nest_end(skb, opts);
diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index 9fc1c62..d974e07 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -297,6 +297,7 @@ static const struct nla_policy fq_codel_policy[TCA_FQ_CODEL_MAX + 1] = {
 	[TCA_FQ_CODEL_ECN]	= { .type = NLA_U32 },
 	[TCA_FQ_CODEL_FLOWS]	= { .type = NLA_U32 },
 	[TCA_FQ_CODEL_QUANTUM]	= { .type = NLA_U32 },
+	[TCA_FQ_CODEL_ECN_TARGET]	= { .type = NLA_U32 },
 };
 
 static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt)
@@ -327,6 +328,13 @@ static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt)
 		q->cparams.target = (target * NSEC_PER_USEC) >> CODEL_SHIFT;
 	}
 
+	if (tb[TCA_FQ_CODEL_ECN_TARGET]) {
+		u64 target = nla_get_u32(tb[TCA_FQ_CODEL_TARGET]);
+
+		q->cparams.ecn_target = (target * NSEC_PER_USEC) >> 
+					CODEL_SHIFT;
+	}
+
 	if (tb[TCA_FQ_CODEL_INTERVAL]) {
 		u64 interval = nla_get_u32(tb[TCA_FQ_CODEL_INTERVAL]);
 
@@ -447,7 +455,9 @@ static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb)
 	    nla_put_u32(skb, TCA_FQ_CODEL_QUANTUM,
 			q->quantum) ||
 	    nla_put_u32(skb, TCA_FQ_CODEL_FLOWS,
-			q->flows_cnt))
+			q->flows_cnt) ||
+	    nla_put_u32(skb, TCA_FQ_CODEL_ECN_TARGET,
+			codel_time_to_us(q->cparams.ecn_target)))
 		goto nla_put_failure;
 
 	nla_nest_end(skb, opts);
-- 
1.7.9.5