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Message-ID: <20231108215322.2845536-1-namhyung@kernel.org>
Date: Wed, 8 Nov 2023 13:53:22 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] locking/percpu-rwsem: Trigger contention tracepoints only if contended
It mistakenly fires lock contention tracepoints always in the writer path.
It should be conditional on the try lock result.
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
kernel/locking/percpu-rwsem.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 185bd1c906b0..6083883c4fe0 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -223,9 +223,10 @@ static bool readers_active_check(struct percpu_rw_semaphore *sem)
void __sched percpu_down_write(struct percpu_rw_semaphore *sem)
{
+ bool contended = false;
+
might_sleep();
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
- trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE);
/* Notify readers to take the slow path. */
rcu_sync_enter(&sem->rss);
@@ -234,8 +235,11 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem)
* Try set sem->block; this provides writer-writer exclusion.
* Having sem->block set makes new readers block.
*/
- if (!__percpu_down_write_trylock(sem))
+ if (!__percpu_down_write_trylock(sem)) {
+ trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE);
percpu_rwsem_wait(sem, /* .reader = */ false);
+ contended = true;
+ }
/* smp_mb() implied by __percpu_down_write_trylock() on success -- D matches A */
@@ -247,7 +251,8 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem)
/* Wait for all active readers to complete. */
rcuwait_wait_event(&sem->writer, readers_active_check(sem), TASK_UNINTERRUPTIBLE);
- trace_contention_end(sem, 0);
+ if (contended)
+ trace_contention_end(sem, 0);
}
EXPORT_SYMBOL_GPL(percpu_down_write);
--
2.42.0.869.gea05f2083d-goog
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