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

Eric Dumazet
2012-06-28T17:07:17Z

From: Eric Dumazet <edumazet@google.com>

At enqueue time, check sojourn time of packet at head of the queue,
and return NET_XMIT_CN instead of NET_XMIT_SUCCESS if this sejourn
time is above codel @target.

This permits local TCP stack to call tcp_enter_cwr() and reduce its cwnd
without drops (for example if ECN is not enabled for the flow)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Dave Taht <dave.taht@bufferbloat.net>
Cc: Tom Herbert <therbert@google.com>
Cc: Matt Mathis <mattmathis@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
---
include/linux/pkt_sched.h | 1 +
include/net/codel.h | 2 +-
net/sched/sch_fq_codel.c | 19 +++++++++++++++----
3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index 32aef0a..4d409a5 100644
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -714,6 +714,7 @@ struct tc_fq_codel_qd_stats {
*/
__u32 new_flows_len; /* count of flows in new list */
__u32 old_flows_len; /* count of flows in old list */
+ __u32 congestion_count;
};

struct tc_fq_codel_cl_stats {
diff --git a/include/net/codel.h b/include/net/codel.h
index 550debf..8c7d6a7 100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -148,7 +148,7 @@ struct codel_vars {
* struct codel_stats - contains codel shared variables and stats
* @maxpacket: largest packet we've seen so far
* @drop_count: temp count of dropped packets in dequeue()
- * ecn_mark: number of packets we ECN marked instead of dropping
+ * @ecn_mark: number of packets we ECN marked instead of dropping
*/
struct codel_stats {
u32 maxpacket;
diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index 9fc1c62..c0485a0 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -62,6 +62,7 @@ struct fq_codel_sched_data {
struct codel_stats cstats;
u32 drop_overlimit;
u32 new_flow_count;
+ u32 congestion_count;

struct list_head new_flows; /* list of new flows */
struct list_head old_flows; /* list of old flows */
@@ -196,16 +197,25 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
flow->deficit = q->quantum;
flow->dropped = 0;
}
- if (++sch->q.qlen < sch->limit)
+ if (++sch->q.qlen < sch->limit) {
+ codel_time_t hdelay = codel_get_enqueue_time(skb) -
+ codel_get_enqueue_time(flow->head);
+
+ /* If this flow is congested, tell the caller ! */
+ if (codel_time_after(hdelay, q->cparams.target)) {
+ q->congestion_count++;
+ return NET_XMIT_CN;
+ }
return NET_XMIT_SUCCESS;
-
+ }
q->drop_overlimit++;
/* Return Congestion Notification only if we dropped a packet
* from this flow.
*/
- if (fq_codel_drop(sch) == idx)
+ if (fq_codel_drop(sch) == idx) {
+ q->congestion_count++;
return NET_XMIT_CN;
-
+ }
/* As we dropped a packet, better let upper stack know this */
qdisc_tree_decrease_qlen(sch, 1);
return NET_XMIT_SUCCESS;
@@ -467,6 +477,7 @@ static int fq_codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)

st.qdisc_stats.maxpacket = q->cstats.maxpacket;
st.qdisc_stats.drop_overlimit = q->drop_overlimit;
+ st.qdisc_stats.congestion_count = q->congestion_count;
st.qdisc_stats.ecn_mark = q->cstats.ecn_mark;
st.qdisc_stats.new_flow_count = q->new_flow_count;