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 <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20251014171907.3554413-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 32e9961570b467b6066f1bb2c00ff1a270e342bc..31561291bc92fd70d4d3ca8f5f7dbc4c94c895a0 100644 (file)
--- a/include/net/sch_generic.h
+++ b/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);
        }
 }