codel: add ce_threshold attribute

For DCTCP or similar ECN based deployments on fabrics with shallow
buffers, hosts are responsible for a good part of the buffering.

This patch adds an optional ce_threshold to codel & fq_codel qdiscs,
so that DCTCP can have feedback from queuing in the host.

A DCTCP enabled egress port simply have a queue occupancy threshold
above which ECT packets get CE mark.

In codel language this translates to a sojourn time, so that one doesn't
have to worry about bytes or bandwidth but delays.

This makes the host an active participant in the health of the whole
network.

This also helps experimenting DCTCP in a setup without DCTCP compliant
fabric.

On following example, ce_threshold is set to 1ms, and we can see from
'ldelay xxx us' that TCP is not trying to go around the 5ms codel
target.

Queue has more capacity to absorb inelastic bursts (say from UDP
traffic), as queues are maintained to an optimal level.

lpaa23:~# ./tc -s -d qd sh dev eth1
qdisc mq 1: dev eth1 root
 Sent 87910654696 bytes 58065331 pkt (dropped 0, overlimits 0 requeues 42961)
 backlog 3108242b 364p requeues 42961
qdisc codel 8063: dev eth1 parent 1:1 limit 1000p target 5.0ms ce_threshold 1.0ms interval 100.0ms
 Sent 7363778701 bytes 4863809 pkt (dropped 0, overlimits 0 requeues 5503)
 rate 2348Mbit 193919pps backlog 255866b 46p requeues 5503
  count 0 lastcount 0 ldelay 1.0ms drop_next 0us
  maxpacket 68130 ecn_mark 0 drop_overlimit 0 ce_mark 72384
qdisc codel 8064: dev eth1 parent 1:2 limit 1000p target 5.0ms ce_threshold 1.0ms interval 100.0ms
 Sent 7636486190 bytes 5043942 pkt (dropped 0, overlimits 0 requeues 5186)
 rate 2319Mbit 191538pps backlog 207418b 64p requeues 5186
  count 0 lastcount 0 ldelay 694us drop_next 0us
  maxpacket 68130 ecn_mark 0 drop_overlimit 0 ce_mark 69873
qdisc codel 8065: dev eth1 parent 1:3 limit 1000p target 5.0ms ce_threshold 1.0ms interval 100.0ms
 Sent 11569360142 bytes 7641602 pkt (dropped 0, overlimits 0 requeues 5554)
 rate 3041Mbit 251096pps backlog 210446b 59p requeues 5554
  count 0 lastcount 0 ldelay 889us drop_next 0us
  maxpacket 68130 ecn_mark 0 drop_overlimit 0 ce_mark 37780
...

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Glenn Judd <glenn.judd@morganstanley.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 2 deletions

diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
index de28f8e968e8..1474b6560fac 100644
--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -6,7 +6,7 @@
  *
  *  Implemented on linux by :
  *  Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
- *  Copyright (C) 2012 Eric Dumazet <edumazet@google.com>
+ *  Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -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_CE_THRESHOLD]= { .type = NLA_U32 },
 };
 
 static int codel_change(struct Qdisc *sch, struct nlattr *opt)
@@ -133,6 +134,12 @@ static int codel_change(struct Qdisc *sch, struct nlattr *opt)
 		q->params.target = ((u64)target * NSEC_PER_USEC) >> CODEL_SHIFT;
 	}
 
+	if (tb[TCA_CODEL_CE_THRESHOLD]) {
+		u64 val = nla_get_u32(tb[TCA_CODEL_CE_THRESHOLD]);
+
+		q->params.ce_threshold = (val * NSEC_PER_USEC) >> CODEL_SHIFT;
+	}
+
 	if (tb[TCA_CODEL_INTERVAL]) {
 		u32 interval = nla_get_u32(tb[TCA_CODEL_INTERVAL]);
 
@@ -201,7 +208,10 @@ static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
 	    nla_put_u32(skb, TCA_CODEL_ECN,
 			q->params.ecn))
 		goto nla_put_failure;
-
+	if (q->params.ce_threshold != CODEL_DISABLED_THRESHOLD &&
+	    nla_put_u32(skb, TCA_CODEL_CE_THRESHOLD,
+			codel_time_to_us(q->params.ce_threshold)))
+		goto nla_put_failure;
 	return nla_nest_end(skb, opts);
 
 nla_put_failure:
@@ -220,6 +230,7 @@ static int codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 		.ldelay		= codel_time_to_us(q->vars.ldelay),
 		.dropping	= q->vars.dropping,
 		.ecn_mark	= q->stats.ecn_mark,
+		.ce_mark	= q->stats.ce_mark,
 	};
 
 	if (q->vars.dropping) {