netdev - [PATCH net-next v3 3/3] net: sched: remove qdisc->empty for lockless qdisc

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Message-ID: <1624344597-11806-4-git-send-email-linyunsheng@huawei.com>
Date:   Tue, 22 Jun 2021 14:49:57 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     <davem@...emloft.net>, <kuba@...nel.org>
CC:     <olteanv@...il.com>, <ast@...nel.org>, <daniel@...earbox.net>,
        <andriin@...com>, <edumazet@...gle.com>, <weiwan@...gle.com>,
        <cong.wang@...edance.com>, <ap420073@...il.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linuxarm@...neuler.org>, <mkl@...gutronix.de>,
        <linux-can@...r.kernel.org>, <jhs@...atatu.com>,
        <xiyou.wangcong@...il.com>, <jiri@...nulli.us>,
        <andrii@...nel.org>, <kafai@...com>, <songliubraving@...com>,
        <yhs@...com>, <john.fastabend@...il.com>, <kpsingh@...nel.org>,
        <bpf@...r.kernel.org>, <jonas.bonn@...rounds.com>,
        <pabeni@...hat.com>, <mzhivich@...mai.com>, <johunt@...mai.com>,
        <albcamus@...il.com>, <kehuan.feng@...il.com>,
        <a.fatoum@...gutronix.de>, <atenart@...nel.org>,
        <alexander.duyck@...il.com>, <hdanton@...a.com>, <jgross@...e.com>,
        <JKosina@...e.com>, <mkubecek@...e.cz>, <bjorn@...nel.org>,
        <alobakin@...me>
Subject: [PATCH net-next v3 3/3] net: sched: remove qdisc->empty for lockless qdisc

As MISSED and DRAINING state are used to indicate a non-empty
qdisc, qdisc->empty is not longer needed, so remove it.

Acked-by: Jakub Kicinski <kuba@...nel.org>
Tested-by: Vladimir Oltean <vladimir.oltean@....com> # flexcan
Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
---
 include/net/sch_generic.h | 13 +++----------
 net/sched/sch_generic.c   |  3 ---
 2 files changed, 3 insertions(+), 13 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 177f240..c99ffe9 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -117,8 +117,6 @@ struct Qdisc {
 	spinlock_t		busylock ____cacheline_aligned_in_smp;
 	spinlock_t		seqlock;
 
-	/* for NOLOCK qdisc, true if there are no enqueued skbs */
-	bool			empty;
 	struct rcu_head		rcu;
 
 	/* private data */
@@ -165,7 +163,7 @@ static inline bool qdisc_is_percpu_stats(const struct Qdisc *q)
 static inline bool qdisc_is_empty(const struct Qdisc *qdisc)
 {
 	if (qdisc_is_percpu_stats(qdisc))
-		return READ_ONCE(qdisc->empty);
+		return nolock_qdisc_is_empty(qdisc);
 	return !READ_ONCE(qdisc->q.qlen);
 }
 
@@ -173,7 +171,7 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 {
 	if (qdisc->flags & TCQ_F_NOLOCK) {
 		if (spin_trylock(&qdisc->seqlock))
-			goto nolock_empty;
+			return true;
 
 		/* If the MISSED flag is set, it means other thread has
 		 * set the MISSED flag before second spin_trylock(), so
@@ -195,12 +193,7 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 		/* Retry again in case other CPU may not see the new flag
 		 * after it releases the lock at the end of qdisc_run_end().
 		 */
-		if (!spin_trylock(&qdisc->seqlock))
-			return false;
-
-nolock_empty:
-		WRITE_ONCE(qdisc->empty, false);
-		return true;
+		return spin_trylock(&qdisc->seqlock);
 	} else if (qdisc_is_running(qdisc)) {
 		return false;
 	}
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 9984ccc..d9ac60f 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -725,8 +725,6 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
 		need_retry = false;
 
 		goto retry;
-	} else {
-		WRITE_ONCE(qdisc->empty, true);
 	}
 
 	return skb;
@@ -927,7 +925,6 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
 	sch->enqueue = ops->enqueue;
 	sch->dequeue = ops->dequeue;
 	sch->dev_queue = dev_queue;
-	sch->empty = true;
 	dev_hold(dev);
 	refcount_set(&sch->refcnt, 1);
 
-- 
2.7.4