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Message-ID: <ZqphRBrI4mlSdER4@localhost.localdomain>
Date: Wed, 31 Jul 2024 18:07:32 +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 v3 13/25] context_tracking, rcu: Rename
rcu_dynticks_task*() into rcu_task*()
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@...nel.org>
> Signed-off-by: Valentin Schneider <vschneid@...hat.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
>
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