Messages in this thread | | | Date | Tue, 27 Feb 2024 19:18:55 -0500 | Subject | Re: [PATCH] locking/percpu-rwsem: Trigger contention tracepoints only if contended | From | Waiman Long <> |
| |
On 2/27/24 18:02, Namhyung Kim wrote: > Hello, > > On Mon, Nov 20, 2023 at 12:28 PM Namhyung Kim <namhyung@kernel.org> wrote: >> Ping! >> >> On Wed, Nov 8, 2023 at 1:53 PM Namhyung Kim <namhyung@kernel.org> wrote: >>> It mistakenly fires lock contention tracepoints always in the writer path. >>> It should be conditional on the try lock result. > Can anybody take a look at this? This makes a large noise > in the lock contention result. > > Thanks, > Namhyung > >>> Signed-off-by: Namhyung Kim <namhyung@kernel.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
Yes, that makes sense. Sorry for missing this patch.
Reviewed-by: Waiman Long <longman@redhat.com>
| |