netdev - [PATCH net-next 1/3] net: sched: avoid unnecessary seqcount operation for lockless qdisc

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Message-ID: <1622170197-27370-2-git-send-email-linyunsheng@huawei.com>
Date:   Fri, 28 May 2021 10:49:55 +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 1/3] net: sched: avoid unnecessary seqcount operation for lockless qdisc

qdisc->running seqcount operation is mainly used to do heuristic
locking on q->busylock for locked qdisc, see qdisc_is_running()
and __dev_xmit_skb().

So avoid doing seqcount operation for qdisc with TCQ_F_NOLOCK
flag.

Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
---
 include/net/sch_generic.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 1e62551..3ed6bcc 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -188,6 +188,7 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 
 nolock_empty:
 		WRITE_ONCE(qdisc->empty, false);
+		return true;
 	} else if (qdisc_is_running(qdisc)) {
 		return false;
 	}
@@ -201,7 +202,6 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 
 static inline void qdisc_run_end(struct Qdisc *qdisc)
 {
-	write_seqcount_end(&qdisc->running);
 	if (qdisc->flags & TCQ_F_NOLOCK) {
 		spin_unlock(&qdisc->seqlock);
 
@@ -210,6 +210,8 @@ static inline void qdisc_run_end(struct Qdisc *qdisc)
 			clear_bit(__QDISC_STATE_MISSED, &qdisc->state);
 			__netif_schedule(qdisc);
 		}
+	} else {
+		write_seqcount_end(&qdisc->running);
 	}
 }
 
-- 
2.7.4