Commit a1bd02e1 authored by Qais Yousef's avatar Qais Yousef Committed by Ingo Molnar
Browse files

sched/rt: Optimize cpupri_find() on non-heterogenous systems 

By introducing a new cpupri_find_fitness() function that takes the
fitness_fn as an argument and only called when asym_system static key is
enabled.

cpupri_find() is now a wrapper function that calls cpupri_find_fitness()
passing NULL as a fitness_fn, hence disabling the logic that handles
fitness by default.

LINK: https://lore.kernel.org/lkml/c0772fca-0a4b-c88d-fdf2-5715fcf8447b@arm.com/


Reported-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarQais Yousef <qais.yousef@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Fixes: 804d402f ("sched/rt: Make RT capacity-aware")
Link: https://lkml.kernel.org/r/20200302132721.8353-4-qais.yousef@arm.com
parent b28bc1e0

kernel/sched/cpupri.c

+8 −2
Original line number Diff line number Diff line
@@ -94,8 +94,14 @@ static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p, 
	return 1;

}



int cpupri_find(struct cpupri *cp, struct task_struct *p,

		struct cpumask *lowest_mask)

{

	return cpupri_find_fitness(cp, p, lowest_mask, NULL);

}



/**

 * cpupri_find - find the best (lowest-pri) CPU in the system

 * cpupri_find_fitness - find the best (lowest-pri) CPU in the system

 * @cp: The cpupri context

 * @p: The task

 * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
@@ -111,7 +117,7 @@ static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p, 
 *

 * Return: (int)bool - CPUs were found

 */

int cpupri_find(struct cpupri *cp, struct task_struct *p,

int cpupri_find_fitness(struct cpupri *cp, struct task_struct *p,

		struct cpumask *lowest_mask,

		bool (*fitness_fn)(struct task_struct *p, int cpu))

{

kernel/sched/cpupri.h

+4 −2
Original line number Diff line number Diff line
@@ -19,6 +19,8 @@ struct cpupri { 


#ifdef CONFIG_SMP

int  cpupri_find(struct cpupri *cp, struct task_struct *p,

		 struct cpumask *lowest_mask);

int  cpupri_find_fitness(struct cpupri *cp, struct task_struct *p,

			 struct cpumask *lowest_mask,

			 bool (*fitness_fn)(struct task_struct *p, int cpu));

void cpupri_set(struct cpupri *cp, int cpu, int pri);

kernel/sched/rt.c

+19 −4
Original line number Diff line number Diff line
@@ -1504,7 +1504,7 @@ static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p) 
	 * let's hope p can move out.

	 */

	if (rq->curr->nr_cpus_allowed == 1 ||

	    !cpupri_find(&rq->rd->cpupri, rq->curr, NULL, NULL))

	    !cpupri_find(&rq->rd->cpupri, rq->curr, NULL))

		return;



	/*
@@ -1512,7 +1512,7 @@ static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p) 
	 * see if it is pushed or pulled somewhere else.

	 */

	if (p->nr_cpus_allowed != 1 &&

	    cpupri_find(&rq->rd->cpupri, p, NULL, NULL))

	    cpupri_find(&rq->rd->cpupri, p, NULL))

		return;



	/*
@@ -1691,6 +1691,7 @@ static int find_lowest_rq(struct task_struct *task) 
	struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);

	int this_cpu = smp_processor_id();

	int cpu      = task_cpu(task);

	int ret;



	/* Make sure the mask is initialized first */

	if (unlikely(!lowest_mask))
@@ -1699,8 +1700,22 @@ static int find_lowest_rq(struct task_struct *task) 
	if (task->nr_cpus_allowed == 1)

		return -1; /* No other targets possible */



	if (!cpupri_find(&task_rq(task)->rd->cpupri, task, lowest_mask,

			 rt_task_fits_capacity))

	/*

	 * If we're on asym system ensure we consider the different capacities

	 * of the CPUs when searching for the lowest_mask.

	 */

	if (static_branch_unlikely(&sched_asym_cpucapacity)) {



		ret = cpupri_find_fitness(&task_rq(task)->rd->cpupri,

					  task, lowest_mask,

					  rt_task_fits_capacity);

	} else {



		ret = cpupri_find(&task_rq(task)->rd->cpupri,

				  task, lowest_mask);

	}



	if (!ret)

		return -1; /* No targets found */



	/*

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