linux-kernel - Re: [PATCH 2/4] locking: Apply contention tracepoints in the slow path

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Message-ID: <20220301094523.5e4bc77d@gandalf.local.home>
Date:   Tue, 1 Mar 2022 09:45:23 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Namhyung Kim <namhyung@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Byungchul Park <byungchul.park@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        bpf@...r.kernel.org, Radoslaw Burny <rburny@...gle.com>
Subject: Re: [PATCH 2/4] locking: Apply contention tracepoints in the slow
 path

On Tue, 1 Mar 2022 10:03:54 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 8555c4efe97c..18b9f4bf6f34 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -1579,6 +1579,8 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
>  
>  	set_current_state(state);
>  
> +	trace_contention_begin(lock, _RET_IP_, LCB_F_RT);

I guess one issue with this is that _RET_IP_ will return the rt_mutex
address if this is not inlined, making the _RET_IP_ rather useless.

Now, if we can pass the _RET_IP_ into __rt_mutex_slowlock() then we could
reference that.

-- Steve


> +
>  	ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
>  	if (likely(!ret))
>  		ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
> @@ -1601,6 +1603,9 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
>  	 * unconditionally. We might have to fix that up.
>  	 */
>  	fixup_rt_mutex_waiters(lock);
> +
> +	trace_contention_end(lock, ret);
> +
>  	return ret;
>  }