Subject: [PATCH] net: sched: remove one pair of atomic operations
From: Eric Dumazet <[email-masked]>
Date: Mon, 18 Oct 2021 17:34:02 -0700

__QDISC_STATE_RUNNING is only set/cleared from contexts owning qdisc lock.

Thus we can use less expensive bit operations, as we were doing
before commit f9eb8aea2a1e ("net_sched: transform qdisc running bit into a seqcount")

Fixes: 29cbcd858283 ("net: sched: Remove Qdisc::running sequence counter")
Signed-off-by: Eric Dumazet <[email-masked]>
Cc: Ahmed S. Darwish <[email-masked]>
Acked-by: Sebastian Andrzej Siewior <[email-masked]>
Tested-by: Toke Høiland-Jørgensen <[email-masked]>
Signed-off-by: Jakub Kicinski <[email-masked]>
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 include/net/sch_generic.h |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -38,10 +38,13 @@ enum qdisc_state_t {
 	__QDISC_STATE_DEACTIVATED,
 	__QDISC_STATE_MISSED,
 	__QDISC_STATE_DRAINING,
+};
+
+enum qdisc_state2_t {
 	/* Only for !TCQ_F_NOLOCK qdisc. Never access it directly.
 	 * Use qdisc_run_begin/end() or qdisc_is_running() instead.
 	 */
-	__QDISC_STATE_RUNNING,
+	__QDISC_STATE2_RUNNING,
 };
 
 #define QDISC_STATE_MISSED	BIT(__QDISC_STATE_MISSED)
@@ -114,6 +117,7 @@ struct Qdisc {
 	struct gnet_stats_basic_sync bstats;
 	struct gnet_stats_queue	qstats;
 	unsigned long		state;
+	unsigned long		state2; /* must be written under qdisc spinlock */
 	struct Qdisc            *next_sched;
 	struct sk_buff_head	skb_bad_txq;
 
@@ -154,7 +158,7 @@ static inline bool qdisc_is_running(stru
 {
 	if (qdisc->flags & TCQ_F_NOLOCK)
 		return spin_is_locked(&qdisc->seqlock);
-	return test_bit(__QDISC_STATE_RUNNING, &qdisc->state);
+	return test_bit(__QDISC_STATE2_RUNNING, &qdisc->state2);
 }
 
 static inline bool nolock_qdisc_is_empty(const struct Qdisc *qdisc)
@@ -217,7 +221,7 @@ static inline bool qdisc_run_begin(struc
 		 */
 		return spin_trylock(&qdisc->seqlock);
 	}
-	return !test_and_set_bit(__QDISC_STATE_RUNNING, &qdisc->state);
+	return !__test_and_set_bit(__QDISC_STATE2_RUNNING, &qdisc->state2);
 }
 
 static inline void qdisc_run_end(struct Qdisc *qdisc)
@@ -229,7 +233,7 @@ static inline void qdisc_run_end(struct
 				      &qdisc->state)))
 			__netif_schedule(qdisc);
 	} else {
-		clear_bit(__QDISC_STATE_RUNNING, &qdisc->state);
+		__clear_bit(__QDISC_STATE2_RUNNING, &qdisc->state2);
 	}
 }