Re: [PATCH 2/2] locking: Apply contention tracepoints in the slow path

From: Boqun Feng <boqun.feng@gmail.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
	Waiman Long <longman@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Byungchul Park <byungchul.park@lge.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Arnd Bergmann <arnd@arndb.de>, Radoslaw Burny <rburny@google.com>,
	linux-arch@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH 2/2] locking: Apply contention tracepoints in the slow path
Date: Fri, 18 Mar 2022 20:55:32 +0800	[thread overview]
Message-ID: <YjSBRNxzaE9c+F/1@boqun-archlinux> (raw)
In-Reply-To: <20220316224548.500123-3-namhyung@kernel.org>

On Wed, Mar 16, 2022 at 03:45:48PM -0700, Namhyung Kim wrote:
[...]
> @@ -209,6 +210,7 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
>  								long timeout)
>  {
>  	struct semaphore_waiter waiter;
> +	bool tracing = false;
>  
>  	list_add_tail(&waiter.list, &sem->wait_list);
>  	waiter.task = current;
> @@ -220,18 +222,28 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
>  		if (unlikely(timeout <= 0))
>  			goto timed_out;
>  		__set_current_state(state);
> +		if (!tracing) {
> +			trace_contention_begin(sem, 0);

This looks a littl ugly ;-/ Maybe we can rename __down_common() to
___down_common() and implement __down_common() as:

	static inline int __sched __down_common(...)
	{
		int ret;
		trace_contention_begin(sem, 0);
		ret = ___down_common(...);
		trace_contention_end(sem, ret);
		return ret;
	}

Thoughts?

Regards,
Boqun

> +			tracing = true;
> +		}
>  		raw_spin_unlock_irq(&sem->lock);
>  		timeout = schedule_timeout(timeout);
>  		raw_spin_lock_irq(&sem->lock);
> -		if (waiter.up)
> +		if (waiter.up) {
> +			trace_contention_end(sem, 0);
>  			return 0;
> +		}
>  	}
>  
>   timed_out:
> +	if (tracing)
> +		trace_contention_end(sem, -ETIME);
>  	list_del(&waiter.list);
>  	return -ETIME;
>  
>   interrupted:
> +	if (tracing)
> +		trace_contention_end(sem, -EINTR);
>  	list_del(&waiter.list);
>  	return -EINTR;
>  }
> -- 
> 2.35.1.894.gb6a874cedc-goog
> 