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Subject[tip: sched/core] sched/rt: Optimize cpupri_find() on non-heterogenous systems
The following commit has been merged into the sched/core branch of tip:

Commit-ID: a1bd02e1f28b1939cac8c64072a0e578c3cbc345
Gitweb: https://git.kernel.org/tip/a1bd02e1f28b1939cac8c64072a0e578c3cbc345
Author: Qais Yousef <qais.yousef@arm.com>
AuthorDate: Mon, 02 Mar 2020 13:27:18
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 06 Mar 2020 12:57:27 +01:00

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: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fixes: 804d402fb6f6 ("sched/rt: Make RT capacity-aware")
Link: https://lkml.kernel.org/r/20200302132721.8353-4-qais.yousef@arm.com
---
kernel/sched/cpupri.c | 10 ++++++++--
kernel/sched/cpupri.h | 6 ++++--
kernel/sched/rt.c | 23 +++++++++++++++++++----
3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c
index 1bcfa19..dd3f16d 100644
--- a/kernel/sched/cpupri.c
+++ b/kernel/sched/cpupri.c
@@ -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))
{
diff --git a/kernel/sched/cpupri.h b/kernel/sched/cpupri.h
index 32dd520..efbb492 100644
--- a/kernel/sched/cpupri.h
+++ b/kernel/sched/cpupri.h
@@ -19,8 +19,10 @@ struct cpupri {

#ifdef CONFIG_SMP
int cpupri_find(struct cpupri *cp, struct task_struct *p,
- struct cpumask *lowest_mask,
- bool (*fitness_fn)(struct task_struct *p, int cpu));
+ 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);
int cpupri_init(struct cpupri *cp);
void cpupri_cleanup(struct cpupri *cp);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index f0071fa..29a8695 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -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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