Commit dc1f7893 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

locking/mutex: Make contention tracepoints more consistent wrt adaptive spinning 



Have the trace_contention_*() tracepoints consistently include
adaptive spinning. In order to differentiate between the spinning and
non-spinning states add LCB_F_MUTEX and combine with LCB_F_SPIN.

The consequence is that a mutex contention can now triggler multiple
_begin() tracepoints before triggering an _end().

Additionally, this fixes one path where mutex would trigger _end()
without ever seeing a _begin().

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
parent ee042be1

include/trace/events/lock.h

+3 −1
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#define LCB_F_WRITE	(1U << 2)

#define LCB_F_RT	(1U << 3)

#define LCB_F_PERCPU	(1U << 4)

#define LCB_F_MUTEX	(1U << 5)





#ifdef CONFIG_LOCKDEP
@@ -113,7 +114,8 @@ TRACE_EVENT(contention_begin, 
				{ LCB_F_READ,		"READ" },

				{ LCB_F_WRITE,		"WRITE" },

				{ LCB_F_RT,		"RT" },

				{ LCB_F_PERCPU,		"PERCPU" }

				{ LCB_F_PERCPU,		"PERCPU" },

				{ LCB_F_MUTEX,		"MUTEX" }

			  ))

);

kernel/locking/mutex.c

+12 −4
Original line number Diff line number Diff line
@@ -602,12 +602,14 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas 
	preempt_disable();

	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);



	trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);

	if (__mutex_trylock(lock) ||

	    mutex_optimistic_spin(lock, ww_ctx, NULL)) {

		/* got the lock, yay! */

		lock_acquired(&lock->dep_map, ip);

		if (ww_ctx)

			ww_mutex_set_context_fastpath(ww, ww_ctx);

		trace_contention_end(lock, 0);

		preempt_enable();

		return 0;

	}
@@ -644,7 +646,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas 
	}



	set_current_state(state);

	trace_contention_begin(lock, 0);

	trace_contention_begin(lock, LCB_F_MUTEX);

	for (;;) {

		bool first;
@@ -684,9 +686,15 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas 
		 * state back to RUNNING and fall through the next schedule(),

		 * or we must see its unlock and acquire.

		 */

		if (__mutex_trylock_or_handoff(lock, first) ||

		    (first && mutex_optimistic_spin(lock, ww_ctx, &waiter)))

		if (__mutex_trylock_or_handoff(lock, first))

			break;



		if (first) {

			trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);

			if (mutex_optimistic_spin(lock, ww_ctx, &waiter))

				break;

			trace_contention_begin(lock, LCB_F_MUTEX);

		}



		raw_spin_lock(&lock->wait_lock);

	}
@@ -723,8 +731,8 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas 
err:

	__set_current_state(TASK_RUNNING);

	__mutex_remove_waiter(lock, &waiter);

	trace_contention_end(lock, ret);

err_early_kill:

	trace_contention_end(lock, ret);

	raw_spin_unlock(&lock->wait_lock);

	debug_mutex_free_waiter(&waiter);

	mutex_release(&lock->dep_map, ip);