Re: [PATCH v10 5/7] sched: Consolidate pick_*_task to task_is_pushable helper

[Metin Kaya]

On 04/06/2024 2:18 pm, Qais Yousef wrote:
> On 05/06/24 21:54, John Stultz wrote:
> > From: Connor O'Brien <connoro@xxxxxxxxxx>
> >
> > This patch consolidates rt and deadline pick_*_task functions to
> > a task_is_pushable() helper
> >
> > This patch was broken out from a larger chain migration
> > patch originally by Connor O'Brien.
> >
> > Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
> > Cc: Qais Yousef <qyousef@xxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
> > Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> > Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> > Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Ben Segall <bsegall@xxxxxxxxxx>
> > Cc: Zimuzo Ezeozue <zezeozue@xxxxxxxxxx>
> > Cc: Youssef Esmat <youssefesmat@xxxxxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxx>
> > Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Waiman Long <longman@xxxxxxxxxx>
> > Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> > Cc: Metin Kaya <Metin.Kaya@xxxxxxx>
> > Cc: Xuewen Yan <xuewen.yan94@xxxxxxxxx>
> > Cc: K Prateek Nayak <kprateek.nayak@xxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: kernel-team@xxxxxxxxxxx
> > Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
> > Tested-by: Metin Kaya <metin.kaya@xxxxxxx>
> > Reviewed-by: Metin Kaya <metin.kaya@xxxxxxx>
> > Reviewed-by: Valentin Schneider <vschneid@xxxxxxxxxx>
> > Signed-off-by: Connor O'Brien <connoro@xxxxxxxxxx>
> > [jstultz: split out from larger chain migration patch,
> >   renamed helper function]
> > Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
> > ---
> > v7:
> > * Split from chain migration patch
> > * Renamed function
> > ---
> >   kernel/sched/deadline.c | 10 +---------
> >   kernel/sched/rt.c       | 11 +----------
> >   kernel/sched/sched.h    | 10 ++++++++++
> >   3 files changed, 12 insertions(+), 19 deletions(-)
> >
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index eaedc69c5e30..ae583a427539 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -2179,14 +2179,6 @@ static void task_fork_dl(struct task_struct *p)
> >   /* Only try algorithms three times */
> >   #define DL_MAX_TRIES 3
> >   
> > -static int pick_dl_task(struct rq *rq, struct task_struct *p, int cpu)
> > -{
> > -	if (!task_on_cpu(rq, p) &&
> > -	    cpumask_test_cpu(cpu, &p->cpus_mask))
> > -		return 1;
> > -	return 0;
> > -}
> > -
> >   /*
> >    * Return the earliest pushable rq's task, which is suitable to be executed
> >    * on the CPU, NULL otherwise:
> > @@ -2205,7 +2197,7 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
> >   	if (next_node) {
> >   		p = __node_2_pdl(next_node);
> >   
> > -		if (pick_dl_task(rq, p, cpu))
> > +		if (task_is_pushable(rq, p, cpu) == 1)
>
> Any reason we're checking specifically for == 1? Could the function later
> return something other than 0 or 1?

I hear you, but just letting you know that `task_is_pushable()` will 
return different non-zero results per upcoming patches in the queue. The 
commit "sched: Fix rt/dl load balancing via chain level balance" will 
make the function look like below (excerpt from `kernel/sched/core.c`):

/*
 * Returns:
 * 1 if chain is pushable and affinity does not prevent pushing to cpu
 * 0 if chain is unpushable
 * -1 if chain is pushable but affinity blocks running on cpu.
 */
int task_is_pushable(struct rq *rq, struct task_struct *p, int cpu)

> It's explaining if 1 could end up meaning something else in the commit message
> and in function docs. Otherwise let's make it a bool and not do explicit check
> for return value.
>
> With this
>
> Reviewed-by: Qais Yousef <qyousef@xxxxxxxxxxx>
>
> >   			return p;
> >   
> >   		next_node = rb_next(next_node);
> > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> > index 975cb49a64dc..8b6fb77e095b 100644
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -1791,15 +1791,6 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
> >   /* Only try algorithms three times */
> >   #define RT_MAX_TRIES 3
> >   
> > -static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
> > -{
> > -	if (!task_on_cpu(rq, p) &&
> > -	    cpumask_test_cpu(cpu, &p->cpus_mask))
> > -		return 1;
> > -
> > -	return 0;
> > -}
> > -
> >   /*
> >    * Return the highest pushable rq's task, which is suitable to be executed
> >    * on the CPU, NULL otherwise
> > @@ -1813,7 +1804,7 @@ static struct task_struct *pick_highest_pushable_task(struct rq *rq, int cpu)
> >   		return NULL;
> >   
> >   	plist_for_each_entry(p, head, pushable_tasks) {
> > -		if (pick_rt_task(rq, p, cpu))
> > +		if (task_is_pushable(rq, p, cpu) == 1)
> >   			return p;
> >   	}
> >   
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 2d41ebe200c7..e46f69ba9ba2 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -3490,6 +3490,16 @@ void move_queued_task_locked(struct rq *rq, struct rq *dst_rq, struct task_struc
> >   	set_task_cpu(task, dst_rq->cpu);
> >   	activate_task(dst_rq, task, 0);
> >   }
> > +
> > +static inline
> > +int task_is_pushable(struct rq *rq, struct task_struct *p, int cpu)
> > +{
> > +	if (!task_on_cpu(rq, p) &&
> > +	    cpumask_test_cpu(cpu, &p->cpus_mask))
> > +		return 1;
> > +
> > +	return 0;
> > +}
> >   #endif
> >   
> >   #endif /* _KERNEL_SCHED_SCHED_H */
> > --
> > 2.45.0.rc1.225.g2a3ae87e7f-goog