Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v4 5/5] locking/rwsem: Update handoff lock events tracking | Date | Mon, 24 Oct 2022 13:44:18 -0400 |
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With the new direct rwsem lock handoff, the corresponding handoff lock events are updated to also track the number of secondary lock handoffs in rwsem_down_read_slowpath() to see how prevalent those handoff events are. The number of primary lock handoffs in the unlock paths is (rwsem_handoff_read + rwsem_handoff_write - rwsem_handoff_rslow).
After running a 96-thread rwsem microbenchmark with equal number of readers and writers on a 2-socket 96-thread system for 40s, the following handoff stats were obtained:
rwsem_handoff_read=189 rwsem_handoff_rslow=1 rwsem_handoff_write=6678 rwsem_handoff_wspin=6681
The number of primary handoffs was 6866, whereas there was only one secondary handoff for this test run.
Signed-off-by: Waiman Long <longman@redhat.com> --- kernel/locking/lock_events_list.h | 6 ++++-- kernel/locking/rwsem.c | 9 +++++---- 2 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/kernel/locking/lock_events_list.h b/kernel/locking/lock_events_list.h index 97fb6f3f840a..04d101767c2c 100644 --- a/kernel/locking/lock_events_list.h +++ b/kernel/locking/lock_events_list.h @@ -63,7 +63,9 @@ LOCK_EVENT(rwsem_rlock) /* # of read locks acquired */ LOCK_EVENT(rwsem_rlock_steal) /* # of read locks by lock stealing */ LOCK_EVENT(rwsem_rlock_fast) /* # of fast read locks acquired */ LOCK_EVENT(rwsem_rlock_fail) /* # of failed read lock acquisitions */ -LOCK_EVENT(rwsem_rlock_handoff) /* # of read lock handoffs */ LOCK_EVENT(rwsem_wlock) /* # of write locks acquired */ LOCK_EVENT(rwsem_wlock_fail) /* # of failed write lock acquisitions */ -LOCK_EVENT(rwsem_wlock_handoff) /* # of write lock handoffs */ +LOCK_EVENT(rwsem_handoff_read) /* # of read lock handoffs */ +LOCK_EVENT(rwsem_handoff_write) /* # of write lock handoffs */ +LOCK_EVENT(rwsem_handoff_rslow) /* # of handoffs in read slowpath */ +LOCK_EVENT(rwsem_handoff_wspin) /* # of handoff spins in write slowpath */ diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 287606aee0e6..46aea1994bf8 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -472,10 +472,8 @@ static void rwsem_mark_wake(struct rw_semaphore *sem, * force the issue. */ if (time_after(jiffies, waiter->timeout)) { - if (!(oldcount & RWSEM_FLAG_HANDOFF)) { + if (!(oldcount & RWSEM_FLAG_HANDOFF)) adjustment -= RWSEM_FLAG_HANDOFF; - lockevent_inc(rwsem_rlock_handoff); - } WRITE_ONCE(waiter->handoff_state, HANDOFF_REQUESTED); } @@ -680,7 +678,6 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, */ if (new & RWSEM_FLAG_HANDOFF) { WRITE_ONCE(first->handoff_state, HANDOFF_REQUESTED); - lockevent_inc(rwsem_wlock_handoff); return false; } @@ -1019,10 +1016,12 @@ static void rwsem_handoff(struct rw_semaphore *sem, long adj, wake_type = RWSEM_WAKE_ANY; adj += RWSEM_WRITER_LOCKED; atomic_long_set(&sem->owner, (long)waiter->task); + lockevent_inc(rwsem_handoff_write); } else { wake_type = RWSEM_WAKE_READ_OWNED; adj += RWSEM_READER_BIAS; __rwsem_set_reader_owned(sem, waiter->task); + lockevent_inc(rwsem_handoff_read); } atomic_long_add(adj, &sem->count); rwsem_mark_wake(sem, wake_type, wake_q); @@ -1128,6 +1127,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat if (rwsem_first_waiter(sem)->type == RWSEM_WAITING_FOR_READ) adjustment = 0; rwsem_handoff(sem, adjustment, &wake_q); + lockevent_inc(rwsem_handoff_rslow); if (!adjustment) { raw_spin_unlock_irq(&sem->wait_lock); @@ -1257,6 +1257,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) preempt_disable(); rwsem_spin_on_owner(sem); preempt_enable(); + lockevent_inc(rwsem_handoff_wspin); } if (READ_ONCE(waiter.handoff_state) == HANDOFF_GRANTED) goto skip_sleep; -- 2.31.1
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