linux-kernel - [tip: locking/core] locking/mutex: Make contention tracepoints more consistent wrt adaptive spinning

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Date:   Tue, 05 Apr 2022 08:36:16 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/mutex: Make contention tracepoints more
 consistent wrt adaptive spinning

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     dc1f7893a70fe403983bd8492f177bf993940e2c
Gitweb:        https://git.kernel.org/tip/dc1f7893a70fe403983bd8492f177bf993940e2c
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 30 Mar 2022 13:06:54 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 05 Apr 2022 10:24:36 +02:00

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: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/trace/events/lock.h |  4 +++-
 kernel/locking/mutex.c      | 16 ++++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h
index b9b6e3e..9ebd081 100644
--- a/include/trace/events/lock.h
+++ b/include/trace/events/lock.h
@@ -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" }
 			  ))
 );
 
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index c88deda..d973fe6 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -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;
 
@@ -684,10 +686,16 @@ __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);
 	}
 	raw_spin_lock(&lock->wait_lock);
@@ -723,8 +731,8 @@ skip_wait:
 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);