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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1773315506; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bu5mWobvX4U3cXiyaUbCa8xpuOximkgmKYMfG+Fla8Q=; b=nh5FAB8TtEr58qotNI9hqlK7o9elx15QlsZorIirz65yTG5vuq0WaNHIlK2GhbLbLCWHtX sf3BDhH2e8K6OF6Gp1caUzDVLIe0dEyOheCOGvZgQ+7cbYdGmHgrKHI6D+jwy9LknsU5IW MVtrimwww8LH9Hq5JTFun2xbeOedeic= From: Usama Arif To: Dmitry Ilvokhin Cc: Usama Arif , Dennis Zhou , Tejun Heo , Christoph Lameter , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2 2/2] locking: Add contended_release tracepoint Date: Thu, 12 Mar 2026 04:38:14 -0700 Message-ID: <20260312113815.2107882-1-usama.arif@linux.dev> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D9D6F2000B X-Stat-Signature: gyg8fwuwyf9xr67imd938c84cktuoi8x X-HE-Tag: 1773315509-17494 X-HE-Meta: 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 eZxqX8ui EJpl/6HkyMOpPM2EPbmqdgDv0CvJ8i1e0zfIG3gMUe5TJOdDEJEiarOBfvOJtqvS3nCCl1Dbk8bqEdXsvpCUO5Lyav3XVF+SrmGHUUNk2BirDt4MWJBN7pgNWVZaYbAuOIOnsm2o/WnWoK2OcB/CZVCoINBqpkXKBhiU6+eva4WQAUhGOW3RBvpGWXLCrXroYxqvFONJV51HJIlBPKWDdISd6iv4sbwsYKArC6KqfXxUCNW9nNI1FPCCVxOr4sm3YBiMWDlVzn7IYwS3+7SFp5p1/owzFWvsCQ9REZ33DrFrEWLpKWRuLAwjYq81D0aUAXcOoVEfAr2MGMOW2VMKPDtrOhw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 10 Mar 2026 17:49:39 +0000 Dmitry Ilvokhin wrote: > Add the contended_release trace event. This tracepoint fires on the > holder side when a contended lock is released, complementing the > existing contention_begin/contention_end tracepoints which fire on the > waiter side. > > This enables correlating lock hold time under contention with waiter > events by lock address. > > Add trace_contended_release() calls to the slowpath unlock paths of > sleepable locks: mutex, rtmutex, semaphore, rwsem, percpu-rwsem, and > RT-specific rwbase locks. Each call site fires only when there are > blocked waiters being woken, except percpu_up_write() which always wakes > via __wake_up(). > > Signed-off-by: Dmitry Ilvokhin > --- > include/trace/events/lock.h | 17 +++++++++++++++++ > kernel/locking/mutex.c | 1 + > kernel/locking/percpu-rwsem.c | 3 +++ > kernel/locking/rtmutex.c | 1 + > kernel/locking/rwbase_rt.c | 8 +++++++- > kernel/locking/rwsem.c | 9 +++++++-- > kernel/locking/semaphore.c | 4 +++- > 7 files changed, 39 insertions(+), 4 deletions(-) > > diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h > index 8e89baa3775f..4f28e41977ec 100644 > --- a/include/trace/events/lock.h > +++ b/include/trace/events/lock.h > @@ -138,6 +138,23 @@ TRACE_EVENT(contention_end, > TP_printk("%p (ret=%d)", __entry->lock_addr, __entry->ret) > ); > > +TRACE_EVENT(contended_release, > + > + TP_PROTO(void *lock), > + > + TP_ARGS(lock), > + > + TP_STRUCT__entry( > + __field(void *, lock_addr) > + ), > + > + TP_fast_assign( > + __entry->lock_addr = lock; > + ), > + > + TP_printk("%p", __entry->lock_addr) > +); > + > #endif /* _TRACE_LOCK_H */ > > /* This part must be outside protection */ > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index 427187ff02db..ff9d07f3e900 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -992,6 +992,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne > if (waiter) { > next = waiter->task; > > + trace_contended_release(lock); > debug_mutex_wake_waiter(lock, waiter); > __clear_task_blocked_on(next, lock); > wake_q_add(&wake_q, next); > diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c > index f3ee7a0d6047..1eee51766aaf 100644 > --- a/kernel/locking/percpu-rwsem.c > +++ b/kernel/locking/percpu-rwsem.c > @@ -263,6 +263,8 @@ void percpu_up_write(struct percpu_rw_semaphore *sem) > { > rwsem_release(&sem->dep_map, _RET_IP_); > > + trace_contended_release(sem); > + Hello! I saw that you mentioned in the commmit message that you do this for only blocked waiters except for percpu_up_write(). We can use waitqueue_active(&sem->waiters) to check for this over here so that its consistent with every other call? > /* > * Signal the writer is done, no fast path yet. > * > @@ -297,6 +299,7 @@ void __percpu_up_read(struct percpu_rw_semaphore *sem) > * writer. > */ > smp_mb(); /* B matches C */ > + trace_contended_release(sem); Should we do this after this_cpu_dec(*sem->read_count)? > /* > * In other words, if they see our decrement (presumably to > * aggregate zero, as that is the only time it matters) they > diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c > index ccaba6148b61..3db8a840b4e8 100644 > --- a/kernel/locking/rtmutex.c > +++ b/kernel/locking/rtmutex.c > @@ -1466,6 +1466,7 @@ static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock) > raw_spin_lock_irqsave(&lock->wait_lock, flags); > } > > + trace_contended_release(lock); > /* > * The wakeup next waiter path does not suffer from the above > * race. See the comments there. > diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c > index 82e078c0665a..081778934b13 100644 > --- a/kernel/locking/rwbase_rt.c > +++ b/kernel/locking/rwbase_rt.c > @@ -162,8 +162,10 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb, > * worst case which can happen is a spurious wakeup. > */ > owner = rt_mutex_owner(rtm); > - if (owner) > + if (owner) { > + trace_contended_release(rwb); > rt_mutex_wake_q_add_task(&wqh, owner, state); > + } > > /* Pairs with the preempt_enable in rt_mutex_wake_up_q() */ > preempt_disable(); > @@ -205,6 +207,8 @@ static inline void rwbase_write_unlock(struct rwbase_rt *rwb) > unsigned long flags; > > raw_spin_lock_irqsave(&rtm->wait_lock, flags); > + if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm)) > + trace_contended_release(rwb); > __rwbase_write_unlock(rwb, WRITER_BIAS, flags); > } > > @@ -214,6 +218,8 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb) > unsigned long flags; > > raw_spin_lock_irqsave(&rtm->wait_lock, flags); > + if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm)) > + trace_contended_release(rwb); > /* Release it and account current as reader */ > __rwbase_write_unlock(rwb, WRITER_BIAS - 1, flags); > } > diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c > index ba4cb74de064..cf7d8e75ad7b 100644 > --- a/kernel/locking/rwsem.c > +++ b/kernel/locking/rwsem.c > @@ -1390,6 +1390,7 @@ static inline void __up_read(struct rw_semaphore *sem) > if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) == > RWSEM_FLAG_WAITERS)) { > clear_nonspinnable(sem); > + trace_contended_release(sem); > rwsem_wake(sem); > } > preempt_enable(); > @@ -1413,8 +1414,10 @@ static inline void __up_write(struct rw_semaphore *sem) > preempt_disable(); > rwsem_clear_owner(sem); > tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count); > - if (unlikely(tmp & RWSEM_FLAG_WAITERS)) > + if (unlikely(tmp & RWSEM_FLAG_WAITERS)) { > + trace_contended_release(sem); > rwsem_wake(sem); > + } > preempt_enable(); > } > > @@ -1437,8 +1440,10 @@ static inline void __downgrade_write(struct rw_semaphore *sem) > tmp = atomic_long_fetch_add_release( > -RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count); > rwsem_set_reader_owned(sem); > - if (tmp & RWSEM_FLAG_WAITERS) > + if (tmp & RWSEM_FLAG_WAITERS) { > + trace_contended_release(sem); > rwsem_downgrade_wake(sem); > + } > preempt_enable(); > } > > diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c > index 74d41433ba13..d46415095dd6 100644 > --- a/kernel/locking/semaphore.c > +++ b/kernel/locking/semaphore.c > @@ -231,8 +231,10 @@ void __sched up(struct semaphore *sem) > else > __up(sem, &wake_q); > raw_spin_unlock_irqrestore(&sem->lock, flags); > - if (!wake_q_empty(&wake_q)) > + if (!wake_q_empty(&wake_q)) { > + trace_contended_release(sem); > wake_up_q(&wake_q); > + } > } > EXPORT_SYMBOL(up); > > -- > 2.52.0 > >