Re: [PATCH v3 13/25] context_tracking, rcu: Rename rcu_dynticks_task*() into rcu_task*()

[Frederic Weisbecker <frederic@kernel.org>]

Le Wed, Jul 24, 2024 at 04:43:13PM +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.
> 
> While at it, flip the suffixes of these helpers. We are not telling
> that we are entering dynticks mode from an RCU-task perspective anymore; we
> are telling that we are exiting RCU-tasks because we are in eqs mode.
> 
> Suggested-by: Frederic Weisbecker <frederic@kernel.org>
> Signed-off-by: Valentin Schneider <vschneid@redhat.com>
> ---
>  kernel/context_tracking.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 8262f57a43636..1c16a7336360f 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -38,24 +38,24 @@ EXPORT_SYMBOL_GPL(context_tracking);
>  #ifdef CONFIG_CONTEXT_TRACKING_IDLE
>  #define TPS(x)  tracepoint_string(x)
>  
> -/* Record the current task on dyntick-idle entry. */
> -static __always_inline void rcu_dynticks_task_enter(void)
> +/* Record the current task on exiting RCU-tasks (dyntick-idle entry). */
> +static __always_inline void rcu_task_exit(void)

So this makes sense.

>  {
>  #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
>  	WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
>  #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
>  }
>  
> -/* Record no current task on dyntick-idle exit. */
> -static __always_inline void rcu_dynticks_task_exit(void)
> +/* Record no current task on entering RCU-tasks (dyntick-idle exit). */
> +static __always_inline void rcu_task_enter(void)

That too.

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

But that eventually doesn't, because it's not about not wathing anymore from
an RCU-TASKS-TRACE perspective. It's actually about adding more heavyweight
ordering to track down RCU-TASKS-TRACE read side while traditional RCU is not
watching. Sorry for understanding it that late.

Oh well. So a more accurate name here would be rcu_task_trace_heavyweight_enter().

>  {
>  #ifdef CONFIG_TASKS_TRACE_RCU
>  	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
> @@ -63,8 +63,8 @@ static __always_inline void rcu_dynticks_task_trace_enter(void)
>  #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
>  }
>  
> -/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
> -static __always_inline void rcu_dynticks_task_trace_exit(void)
> +/* Turn off heavyweight RCU tasks trace readers on kernel entry. */
> +static __always_inline void rcu_task_trace_enter(void)

And rcu_task_trace_heavyweight_exit().

Thanks!

>  {
>  #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_exit();  // Before CT state update!
>  	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_enter();  // After CT state update!
>  	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & CT_RCU_WATCHING));
>  }
>  
> @@ -149,7 +149,7 @@ static void noinstr ct_kernel_exit(bool user, int offset)
>  	// RCU is watching here ...
>  	ct_kernel_exit_state(offset);
>  	// ... but is no longer watching here.
> -	rcu_dynticks_task_enter();
> +	rcu_task_exit();
>  }
>  
>  /*
> @@ -173,7 +173,7 @@ static void noinstr ct_kernel_enter(bool user, int offset)
>  		ct->nesting++;
>  		return;
>  	}
> -	rcu_dynticks_task_exit();
> +	rcu_task_enter();
>  	// RCU is not watching here ...
>  	ct_kernel_enter_state(offset);
>  	// ... but is watching here.
> @@ -240,7 +240,7 @@ void noinstr ct_nmi_exit(void)
>  	// ... but is no longer watching here.
>  
>  	if (!in_nmi())
> -		rcu_dynticks_task_enter();
> +		rcu_task_exit();
>  }
>  
>  /**
> @@ -274,7 +274,7 @@ void noinstr ct_nmi_enter(void)
>  	if (rcu_dynticks_curr_cpu_in_eqs()) {
>  
>  		if (!in_nmi())
> -			rcu_dynticks_task_exit();
> +			rcu_task_enter();
>  
>  		// RCU is not watching here ...
>  		ct_kernel_enter_state(CT_RCU_WATCHING);
> -- 
> 2.43.0
>