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

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Message-ID: <20240814120655.GA1412760@neeraj.linux>
Date: Wed, 14 Aug 2024 17:36:55 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Valentin Schneider <vschneid@...hat.com>, 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*()

On Wed, Jul 31, 2024 at 06:07:32PM +0200, Frederic Weisbecker wrote:
> 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().
> 

I have updated it here [1]. Please let me know if something looks
incorrect.


[1] https://git.kernel.org/pub/scm/linux/kernel/git/neeraj.upadhyay/linux-rcu.git/commit/?h=next.14.08.24a&id=cfc22b9f1572b137dd9f36da831dd7b69c9fe352

- Neeraj

> 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
> >