Messages in this thread | | | From | Namhyung Kim <> | Date | Tue, 27 Feb 2024 16:49:45 -0800 | Subject | Re: [PATCH] locking/percpu-rwsem: Trigger contention tracepoints only if contended |
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On Tue, Feb 27, 2024 at 4:19 PM Waiman Long <longman@redhat.com> wrote: > > > 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>
Thanks for your review. Namhyung
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