locking/rwsem: Enable lock event counting

Add lock event counting calls so that we can track the number of lock
events happening in the rwsem code.

With CONFIG_LOCK_EVENT_COUNTS on and booting a 4-socket 112-thread x86-64
system, the rwsem counts after system bootup were as follows:

  rwsem_opt_fail=261
  rwsem_opt_wlock=50636
  rwsem_rlock=445
  rwsem_rlock_fail=0
  rwsem_rlock_fast=22
  rwsem_rtrylock=810144
  rwsem_sleep_reader=441
  rwsem_sleep_writer=310
  rwsem_wake_reader=355
  rwsem_wake_writer=2335
  rwsem_wlock=261
  rwsem_wlock_fail=0
  rwsem_wtrylock=20583

It can be seen that most of the lock acquisitions in the slowpath were
write-locks in the optimistic spinning code path with no sleeping at
all. For this system, over 97% of the locks are acquired via optimistic
spinning. It illustrates the importance of optimistic spinning in
improving the performance of rwsem.

Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-11-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index f6198e1a58f6..6b3ee9948bf1 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -147,6 +147,7 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem,
 			 * will notice the queued writer.
 			 */
 			wake_q_add(wake_q, waiter->task);
+			lockevent_inc(rwsem_wake_writer);
 		}
 
 		return;
@@ -214,6 +215,7 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem,
 	}
 
 	adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;
+	lockevent_cond_inc(rwsem_wake_reader, woken);
 	if (list_empty(&sem->wait_list)) {
 		/* hit end of list above */
 		adjustment -= RWSEM_WAITING_BIAS;
@@ -265,6 +267,7 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
 		if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
 					count + RWSEM_ACTIVE_WRITE_BIAS)) {
 			rwsem_set_owner(sem);
+			lockevent_inc(rwsem_opt_wlock);
 			return true;
 		}
 	}
@@ -389,6 +392,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
 	osq_unlock(&sem->osq);
 done:
 	preempt_enable();
+	lockevent_cond_inc(rwsem_opt_fail, !taken);
 	return taken;
 }
 
@@ -436,6 +440,7 @@ __rwsem_down_read_failed_common(struct rw_semaphore *sem, int state)
 		if (atomic_long_read(&sem->count) >= 0) {
 			raw_spin_unlock_irq(&sem->wait_lock);
 			rwsem_set_reader_owned(sem);
+			lockevent_inc(rwsem_rlock_fast);
 			return sem;
 		}
 		adjustment += RWSEM_WAITING_BIAS;
@@ -472,9 +477,11 @@ __rwsem_down_read_failed_common(struct rw_semaphore *sem, int state)
 			break;
 		}
 		schedule();
+		lockevent_inc(rwsem_sleep_reader);
 	}
 
 	__set_current_state(TASK_RUNNING);
+	lockevent_inc(rwsem_rlock);
 	return sem;
 out_nolock:
 	list_del(&waiter.list);
@@ -482,6 +489,7 @@ out_nolock:
 		atomic_long_add(-RWSEM_WAITING_BIAS, &sem->count);
 	raw_spin_unlock_irq(&sem->wait_lock);
 	__set_current_state(TASK_RUNNING);
+	lockevent_inc(rwsem_rlock_fail);
 	return ERR_PTR(-EINTR);
 }
 
@@ -575,6 +583,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
 				goto out_nolock;
 
 			schedule();
+			lockevent_inc(rwsem_sleep_writer);
 			set_current_state(state);
 		} while ((count = atomic_long_read(&sem->count)) & RWSEM_ACTIVE_MASK);
 
@@ -583,6 +592,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
 	__set_current_state(TASK_RUNNING);
 	list_del(&waiter.list);
 	raw_spin_unlock_irq(&sem->wait_lock);
+	lockevent_inc(rwsem_wlock);
 
 	return ret;
 
@@ -596,6 +606,7 @@ out_nolock:
 		__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
 	raw_spin_unlock_irq(&sem->wait_lock);
 	wake_up_q(&wake_q);
+	lockevent_inc(rwsem_wlock_fail);
 
 	return ERR_PTR(-EINTR);
 }