linux-kernel - Re: [PATCH v2] sched/rt: Clean up usage of rt

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Message-ID: <20240527173703.52wsstp5dnczaxrv@airbuntu>
Date: Mon, 27 May 2024 18:37:03 +0100
From: Qais Yousef <qyousef@...alina.io>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-mm@...ck.org, Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v2] sched/rt: Clean up usage of rt_task()

On 05/23/24 11:45, Steven Rostedt wrote:
> On Wed, 15 May 2024 23:05:36 +0100
> Qais Yousef <qyousef@...alina.io> wrote:
> > diff --git a/include/linux/sched/deadline.h b/include/linux/sched/deadline.h
> > index df3aca89d4f5..5cb88b748ad6 100644
> > --- a/include/linux/sched/deadline.h
> > +++ b/include/linux/sched/deadline.h
> > @@ -10,8 +10,6 @@
> >  
> >  #include <linux/sched.h>
> >  
> > -#define MAX_DL_PRIO		0
> > -
> >  static inline int dl_prio(int prio)
> >  {
> >  	if (unlikely(prio < MAX_DL_PRIO))
> > @@ -19,6 +17,10 @@ static inline int dl_prio(int prio)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * Returns true if a task has a priority that belongs to DL class. PI-boosted
> > + * tasks will return true. Use dl_policy() to ignore PI-boosted tasks.
> > + */
> >  static inline int dl_task(struct task_struct *p)
> >  {
> >  	return dl_prio(p->prio);
> > diff --git a/include/linux/sched/prio.h b/include/linux/sched/prio.h
> > index ab83d85e1183..6ab43b4f72f9 100644
> > --- a/include/linux/sched/prio.h
> > +++ b/include/linux/sched/prio.h
> > @@ -14,6 +14,7 @@
> >   */
> >  
> >  #define MAX_RT_PRIO		100
> > +#define MAX_DL_PRIO		0
> >  
> >  #define MAX_PRIO		(MAX_RT_PRIO + NICE_WIDTH)
> >  #define DEFAULT_PRIO		(MAX_RT_PRIO + NICE_WIDTH / 2)
> > diff --git a/include/linux/sched/rt.h b/include/linux/sched/rt.h
> > index b2b9e6eb9683..a055dd68a77c 100644
> > --- a/include/linux/sched/rt.h
> > +++ b/include/linux/sched/rt.h
> > @@ -7,18 +7,43 @@
> >  struct task_struct;
> >  
> >  static inline int rt_prio(int prio)
> > +{
> > +	if (unlikely(prio < MAX_RT_PRIO && prio >= MAX_DL_PRIO))
> > +		return 1;
> > +	return 0;
> > +}
> > +
> > +static inline int realtime_prio(int prio)
> >  {
> >  	if (unlikely(prio < MAX_RT_PRIO))
> >  		return 1;
> >  	return 0;
> >  }
> 
> I'm thinking we should change the above to bool (separate patch), as
> returning an int may give one the impression that it returns the actual
> priority number. Having it return bool will clear that up.
> 
> In fact, if we are touching theses functions, might as well change all of
> them to bool when returning true/false. Just to make it easier to
> understand what they are doing.

I can add a patch on top, sure.

> 
> >  
> > +/*
> > + * Returns true if a task has a priority that belongs to RT class. PI-boosted
> > + * tasks will return true. Use rt_policy() to ignore PI-boosted tasks.
> > + */
> >  static inline int rt_task(struct task_struct *p)
> >  {
> >  	return rt_prio(p->prio);
> >  }
> >  
> > -static inline bool task_is_realtime(struct task_struct *tsk)
> > +/*
> > + * Returns true if a task has a priority that belongs to RT or DL classes.
> > + * PI-boosted tasks will return true. Use realtime_task_policy() to ignore
> > + * PI-boosted tasks.
> > + */
> > +static inline int realtime_task(struct task_struct *p)
> > +{
> > +	return realtime_prio(p->prio);
> > +}
> > +
> > +/*
> > + * Returns true if a task has a policy that belongs to RT or DL classes.
> > + * PI-boosted tasks will return false.
> > + */
> > +static inline bool realtime_task_policy(struct task_struct *tsk)
> >  {
> >  	int policy = tsk->policy;
> >  
> 
> 
> 
> > diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
> > index 0469a04a355f..19d737742e29 100644
> > --- a/kernel/trace/trace_sched_wakeup.c
> > +++ b/kernel/trace/trace_sched_wakeup.c
> > @@ -545,7 +545,7 @@ probe_wakeup(void *ignore, struct task_struct *p)
> >  	 *  - wakeup_dl handles tasks belonging to sched_dl class only.
> >  	 */
> >  	if (tracing_dl || (wakeup_dl && !dl_task(p)) ||
> > -	    (wakeup_rt && !dl_task(p) && !rt_task(p)) ||
> > +	    (wakeup_rt && !realtime_task(p)) ||
> >  	    (!dl_task(p) && (p->prio >= wakeup_prio || p->prio >= current->prio)))
> >  		return;
> >  
> 
> Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

Thanks!

--
Qais Yousef

> 
>