net_sched: sch_cake: Add drop reasons

Add three qdisc-specific drop reasons and use them in sch_cake:

 1) SKB_DROP_REASON_QDISC_OVERLIMIT
    Whenever the total queue limit for a qdisc instance is exceeded
    and a packet is dropped to make room.

 2) SKB_DROP_REASON_QDISC_CONGESTED
    Whenever a packet is dropped by the qdisc AQM algorithm because
    congestion is detected.

 3) SKB_DROP_REASON_CAKE_FLOOD
    Whenever a packet is dropped by the flood protection part of the
    CAKE AQM algorithm (BLUE).

Also use the existing SKB_DROP_REASON_QUEUE_PURGE in cake_clear_tin().

Reasons show up as:

perf record -a -e skb:kfree_skb sleep 1; perf script

          iperf3     665 [005]   848.656964: skb:kfree_skb: skbaddr=0xffff98168a333500 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x10f0 reason: QDISC_OVERLIMIT
         swapper       0 [001]   909.166055: skb:kfree_skb: skbaddr=0xffff98168280cee0 rx_sk=(nil) protocol=34525 location=cake_dequeue+0x5ef reason: QDISC_CONGESTED

Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Dave Taht <dave.taht@gmail.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/20241211-cake-drop-reason-v2-1-920afadf4d1b@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 23 insertions, 20 deletions

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 8d8b2db4653c..deb0925f536d 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -484,13 +484,14 @@ static bool cobalt_queue_empty(struct cobalt_vars *vars,
 /* Call this with a freshly dequeued packet for possible congestion marking.
  * Returns true as an instruction to drop the packet, false for delivery.
  */
-static bool cobalt_should_drop(struct cobalt_vars *vars,
-			       struct cobalt_params *p,
-			       ktime_t now,
-			       struct sk_buff *skb,
-			       u32 bulk_flows)
+static enum skb_drop_reason cobalt_should_drop(struct cobalt_vars *vars,
+					       struct cobalt_params *p,
+					       ktime_t now,
+					       struct sk_buff *skb,
+					       u32 bulk_flows)
 {
-	bool next_due, over_target, drop = false;
+	enum skb_drop_reason reason = SKB_NOT_DROPPED_YET;
+	bool next_due, over_target;
 	ktime_t schedule;
 	u64 sojourn;
 
@@ -533,7 +534,8 @@ static bool cobalt_should_drop(struct cobalt_vars *vars,
 
 	if (next_due && vars->dropping) {
 		/* Use ECN mark if possible, otherwise drop */
-		drop = !(vars->ecn_marked = INET_ECN_set_ce(skb));
+		if (!(vars->ecn_marked = INET_ECN_set_ce(skb)))
+			reason = SKB_DROP_REASON_QDISC_CONGESTED;
 
 		vars->count++;
 		if (!vars->count)
@@ -556,16 +558,17 @@ static bool cobalt_should_drop(struct cobalt_vars *vars,
 	}
 
 	/* Simple BLUE implementation.  Lack of ECN is deliberate. */
-	if (vars->p_drop)
-		drop |= (get_random_u32() < vars->p_drop);
+	if (vars->p_drop && reason == SKB_NOT_DROPPED_YET &&
+	    get_random_u32() < vars->p_drop)
+		reason = SKB_DROP_REASON_CAKE_FLOOD;
 
 	/* Overload the drop_next field as an activity timeout */
 	if (!vars->count)
 		vars->drop_next = ktime_add_ns(now, p->interval);
-	else if (ktime_to_ns(schedule) > 0 && !drop)
+	else if (ktime_to_ns(schedule) > 0 && reason == SKB_NOT_DROPPED_YET)
 		vars->drop_next = now;
 
-	return drop;
+	return reason;
 }
 
 static bool cake_update_flowkeys(struct flow_keys *keys,
@@ -1528,12 +1531,11 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
 
 	flow->dropped++;
 	b->tin_dropped++;
-	sch->qstats.drops++;
 
 	if (q->rate_flags & CAKE_FLAG_INGRESS)
 		cake_advance_shaper(q, b, skb, now, true);
 
-	__qdisc_drop(skb, to_free);
+	qdisc_drop_reason(skb, sch, to_free, SKB_DROP_REASON_QDISC_OVERLIMIT);
 	sch->q.qlen--;
 	qdisc_tree_reduce_backlog(sch, 1, len);
 
@@ -1926,7 +1928,7 @@ static void cake_clear_tin(struct Qdisc *sch, u16 tin)
 	q->cur_tin = tin;
 	for (q->cur_flow = 0; q->cur_flow < CAKE_QUEUES; q->cur_flow++)
 		while (!!(skb = cake_dequeue_one(sch)))
-			kfree_skb(skb);
+			kfree_skb_reason(skb, SKB_DROP_REASON_QUEUE_PURGE);
 }
 
 static struct sk_buff *cake_dequeue(struct Qdisc *sch)
@@ -1934,6 +1936,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 	struct cake_sched_data *q = qdisc_priv(sch);
 	struct cake_tin_data *b = &q->tins[q->cur_tin];
 	struct cake_host *srchost, *dsthost;
+	enum skb_drop_reason reason;
 	ktime_t now = ktime_get();
 	struct cake_flow *flow;
 	struct list_head *head;
@@ -2143,12 +2146,12 @@ retry:
 			goto begin;
 		}
 
+		reason = cobalt_should_drop(&flow->cvars, &b->cparams, now, skb,
+					    (b->bulk_flow_count *
+					     !!(q->rate_flags &
+						CAKE_FLAG_INGRESS)));
 		/* Last packet in queue may be marked, shouldn't be dropped */
-		if (!cobalt_should_drop(&flow->cvars, &b->cparams, now, skb,
-					(b->bulk_flow_count *
-					 !!(q->rate_flags &
-					    CAKE_FLAG_INGRESS))) ||
-		    !flow->head)
+		if (reason == SKB_NOT_DROPPED_YET || !flow->head)
 			break;
 
 		/* drop this packet, get another one */
@@ -2162,7 +2165,7 @@ retry:
 		b->tin_dropped++;
 		qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
 		qdisc_qstats_drop(sch);
-		kfree_skb(skb);
+		kfree_skb_reason(skb, reason);
 		if (q->rate_flags & CAKE_FLAG_INGRESS)
 			goto retry;
 	}