netdev - [PATCH v2 net-next 7/7] net/sched: taprio: replace safety precautions with comments

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Date:   Thu, 15 Sep 2022 13:50:46 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Voon Weifeng <weifeng.voon@...el.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 net-next 7/7] net/sched: taprio: replace safety precautions with comments

The WARN_ON_ONCE() checks introduced in commit 13511704f8d7 ("net:
taprio offload: enforce qdisc to netdev queue mapping") take a small
toll on performance, but otherwise, the conditions are never expected to
happen. Replace them with comments, such that the information is still
conveyed to developers.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
v1->v2: patch is new

 net/sched/sch_taprio.c | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index bc93f709d354..8ae454052201 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -433,6 +433,9 @@ static int taprio_enqueue_one(struct sk_buff *skb, struct Qdisc *sch,
 	return qdisc_enqueue(skb, child, to_free);
 }
 
+/* Will not be called in the full offload case, since the TX queues are
+ * attached to the Qdisc created using qdisc_create_dflt()
+ */
 static int taprio_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			  struct sk_buff **to_free)
 {
@@ -440,11 +443,6 @@ static int taprio_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	struct Qdisc *child;
 	int queue;
 
-	if (unlikely(FULL_OFFLOAD_IS_ENABLED(q->flags))) {
-		WARN_ONCE(1, "Trying to enqueue skb into the root of a taprio qdisc configured with full offload\n");
-		return qdisc_drop(skb, sch, to_free);
-	}
-
 	queue = skb_get_queue_mapping(skb);
 
 	child = q->qdiscs[queue];
@@ -490,6 +488,9 @@ static int taprio_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	return taprio_enqueue_one(skb, sch, child, to_free);
 }
 
+/* Will not be called in the full offload case, since the TX queues are
+ * attached to the Qdisc created using qdisc_create_dflt()
+ */
 static struct sk_buff *taprio_peek(struct Qdisc *sch)
 {
 	struct taprio_sched *q = qdisc_priv(sch);
@@ -499,11 +500,6 @@ static struct sk_buff *taprio_peek(struct Qdisc *sch)
 	u32 gate_mask;
 	int i;
 
-	if (unlikely(FULL_OFFLOAD_IS_ENABLED(q->flags))) {
-		WARN_ONCE(1, "Trying to peek into the root of a taprio qdisc configured with full offload\n");
-		return NULL;
-	}
-
 	rcu_read_lock();
 	entry = rcu_dereference(q->current_entry);
 	gate_mask = entry ? entry->gate_mask : TAPRIO_ALL_GATES_OPEN;
@@ -546,6 +542,9 @@ static void taprio_set_budget(struct taprio_sched *q, struct sched_entry *entry)
 			     atomic64_read(&q->picos_per_byte)));
 }
 
+/* Will not be called in the full offload case, since the TX queues are
+ * attached to the Qdisc created using qdisc_create_dflt()
+ */
 static struct sk_buff *taprio_dequeue(struct Qdisc *sch)
 {
 	struct taprio_sched *q = qdisc_priv(sch);
@@ -555,11 +554,6 @@ static struct sk_buff *taprio_dequeue(struct Qdisc *sch)
 	u32 gate_mask;
 	int i;
 
-	if (unlikely(FULL_OFFLOAD_IS_ENABLED(q->flags))) {
-		WARN_ONCE(1, "Trying to dequeue from the root of a taprio qdisc configured with full offload\n");
-		return NULL;
-	}
-
 	rcu_read_lock();
 	entry = rcu_dereference(q->current_entry);
 	/* if there's no entry, it means that the schedule didn't
-- 
2.34.1