net: sched: claim one cache line in Qdisc

Replace state2 field with a boolean.

Move it to a hole between qstats and state so that
we shrink Qdisc by a full cache line.

Signed-off-by: Eric Dumazet <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
Reviewed-by: Toke Høiland-Jørgensen <[email protected]>
Tested-by: Jamal Hadi Salim <[email protected]>
Acked-by: Jamal Hadi Salim <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: edumazet

include/net/sch_generic.h

@@ -41,13 +41,6 @@ enum qdisc_state_t {
 	__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_STATE2_RUNNING,
-};
-
 #define QDISC_STATE_MISSED	BIT(__QDISC_STATE_MISSED)
 #define QDISC_STATE_DRAINING	BIT(__QDISC_STATE_DRAINING)
 
@@ -117,8 +110,8 @@ struct Qdisc {
 	struct qdisc_skb_head	q;
 	struct gnet_stats_basic_sync bstats;
 	struct gnet_stats_queue	qstats;
+	bool			running; /* must be written under qdisc spinlock */
 	unsigned long		state;
-	unsigned long		state2; /* must be written under qdisc spinlock */
 	struct Qdisc            *next_sched;
 	struct sk_buff_head	skb_bad_txq;
 
@@ -167,7 +160,7 @@ static inline bool qdisc_is_running(struct Qdisc *qdisc)
 {
 	if (qdisc->flags & TCQ_F_NOLOCK)
 		return spin_is_locked(&qdisc->seqlock);
-	return test_bit(__QDISC_STATE2_RUNNING, &qdisc->state2);
+	return READ_ONCE(qdisc->running);
 }
 
 static inline bool nolock_qdisc_is_empty(const struct Qdisc *qdisc)
@@ -210,7 +203,10 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 		 */
 		return spin_trylock(&qdisc->seqlock);
 	}
-	return !__test_and_set_bit(__QDISC_STATE2_RUNNING, &qdisc->state2);
+	if (READ_ONCE(qdisc->running))
+		return false;
+	WRITE_ONCE(qdisc->running, true);
+	return true;
 }
 
 static inline void qdisc_run_end(struct Qdisc *qdisc)
@@ -228,7 +224,7 @@ static inline void qdisc_run_end(struct Qdisc *qdisc)
 				      &qdisc->state)))
 			__netif_schedule(qdisc);
 	} else {
-		__clear_bit(__QDISC_STATE2_RUNNING, &qdisc->state2);
+		WRITE_ONCE(qdisc->running, false);
 	}
 }