netdev - [PATCH net-next 2/2] fq_codel: Kill useless per-flow dropped statistic

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Date:   Sat,  3 Aug 2019 16:37:29 -0700
From:   Dave Taht <dave.taht@...il.com>
To:     netdev@...r.kernel.org
Cc:     Dave Taht <dave.taht@...il.com>
Subject: [PATCH net-next 2/2] fq_codel: Kill useless per-flow dropped statistic

It is almost impossible to get anything other than a 0 out of
flow->dropped statistic with a tc class dump, as it resets to 0
on every round.

It also conflates ecn marks with drops.

It would have been useful had it kept a cumulative drop count, but
it doesn't. This patch doesn't change the API, it just stops
tracking a stat and state that is impossible to measure and nobody
uses.

Signed-off-by: Dave Taht <dave.taht@...il.com>

---
 net/sched/sch_fq_codel.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index d67b2c40e6e6..9edd0f495001 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -45,7 +45,6 @@ struct fq_codel_flow {
 	struct sk_buff	  *tail;
 	struct list_head  flowchain;
 	int		  deficit;
-	u32		  dropped; /* number of drops (or ECN marks) on this flow */
 	struct codel_vars cvars;
 }; /* please try to keep this structure <= 64 bytes */
 
@@ -175,7 +174,6 @@ static unsigned int fq_codel_drop(struct Qdisc *sch, unsigned int max_packets,
 
 	/* Tell codel to increase its signal strength also */
 	flow->cvars.count += i;
-	flow->dropped += i;
 	q->backlogs[idx] -= len;
 	q->memory_usage -= mem;
 	sch->qstats.drops += i;
@@ -213,7 +211,6 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		list_add_tail(&flow->flowchain, &q->new_flows);
 		q->new_flow_count++;
 		flow->deficit = q->quantum;
-		flow->dropped = 0;
 	}
 	get_codel_cb(skb)->mem_usage = skb->truesize;
 	q->memory_usage += get_codel_cb(skb)->mem_usage;
@@ -312,9 +309,6 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
 			    &flow->cvars, &q->cstats, qdisc_pkt_len,
 			    codel_get_enqueue_time, drop_func, dequeue_func);
 
-	flow->dropped += q->cstats.drop_count - prev_drop_count;
-	flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
-
 	if (!skb) {
 		/* force a pass through old_flows to prevent starvation */
 		if ((head == &q->new_flows) && !list_empty(&q->old_flows))
@@ -660,7 +654,7 @@ static int fq_codel_dump_class_stats(struct Qdisc *sch, unsigned long cl,
 			sch_tree_unlock(sch);
 		}
 		qs.backlog = q->backlogs[idx];
-		qs.drops = flow->dropped;
+		qs.drops = 0;
 	}
 	if (gnet_stats_copy_queue(d, NULL, &qs, qs.qlen) < 0)
 		return -1;
-- 
2.17.1