linux-kernel - Re: [PATCH v2 13/27] context_tracking, rcu: Rename rcu_dynticks_task*() into rcu

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Message-ID: <ZjuOp78k9E0el_Rn@localhost.localdomain>
Date: Wed, 8 May 2024 16:39:35 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Valentin Schneider <vschneid@...hat.com>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Neeraj Upadhyay <quic_neeraju@...cinc.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH v2 13/27] context_tracking, rcu: Rename
 rcu_dynticks_task*() into rcu_task*()

Le Tue, Apr 30, 2024 at 11:17:17AM +0200, Valentin Schneider a écrit :
> The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
> RCU_WATCHING, and the 'dynticks' prefix can be dropped without losing any
> meaning.
> 
> Suggested-by: Frederic Weisbecker <frederic@...nel.org>
> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
> ---
>  kernel/context_tracking.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 647939b0befd9..9c8f7b9191cd4 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -39,7 +39,7 @@ EXPORT_SYMBOL_GPL(context_tracking);
>  #define TPS(x)  tracepoint_string(x)
>  
>  /* Record the current task on dyntick-idle entry. */
> -static __always_inline void rcu_dynticks_task_enter(void)
> +static __always_inline void rcu_task_enter(void)

On a second thought, this should be the reverse. We are not
telling anymore that we are entering dynticks mode from an
RCU-task perspective. We are telling that we are exiting RCU-tasks
because we are in eqs mode (even though this is mostly a concern
for nohz_full here, as idle tasks are entirely quiescent states
but anyway...).

So this should be s/rcu_dynticks_task_enter/rcu_task_exit

>  {
>  #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
>  	WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
> @@ -47,7 +47,7 @@ static __always_inline void rcu_dynticks_task_enter(void)
>  }
>  
>  /* Record no current task on dyntick-idle exit. */
> -static __always_inline void rcu_dynticks_task_exit(void)
> +static __always_inline void rcu_task_exit(void)

And s/rcu_dynticks_task_exit/rcu_task_enter

>  {
>  #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
>  	WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
> @@ -55,7 +55,7 @@ static __always_inline void rcu_dynticks_task_exit(void)
>  }
>  
>  /* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
> -static __always_inline void rcu_dynticks_task_trace_enter(void)
> +static __always_inline void rcu_task_trace_enter(void)

The same reverse naming goes for task_trace (even though I can't make
sense right now of what the barrier it implies orders exactly, but that's
another story)

>  {
>  #ifdef CONFIG_TASKS_TRACE_RCU
>  	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
> @@ -64,7 +64,7 @@ static __always_inline void rcu_dynticks_task_trace_enter(void)
>  }
>  
>  /* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
> -static __always_inline void rcu_dynticks_task_trace_exit(void)
> +static __always_inline void rcu_task_trace_exit(void)
>  {
>  #ifdef CONFIG_TASKS_TRACE_RCU
>  	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
> @@ -87,7 +87,7 @@ static noinstr void ct_kernel_exit_state(int offset)
>  	 * critical sections, and we also must force ordering with the
>  	 * next idle sojourn.
>  	 */
> -	rcu_dynticks_task_trace_enter();  // Before ->dynticks update!
> +	rcu_task_trace_enter();  // Before ->dynticks update!

s/->dynticks/->state

>  	seq = ct_state_inc(offset);
>  	// RCU is no longer watching.  Better be in extended quiescent state!
>  	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & CT_RCU_WATCHING));
> @@ -109,7 +109,7 @@ static noinstr void ct_kernel_enter_state(int offset)
>  	 */
>  	seq = ct_state_inc(offset);
>  	// RCU is now watching.  Better not be in an extended quiescent state!
> -	rcu_dynticks_task_trace_exit();  // After ->dynticks update!
> +	rcu_task_trace_exit();  // After ->dynticks update!

ditto

Thanks!