[PATCH 2/4] sched/fair: cleanup loop_max and loop_break

Vincent Guittot
2022-08-25T12:27:49Z

sched_nr_migrate_break is set to a fix value and never changes so we can
replace it by a define SCHED_NR_MIGRATE_BREAK.

Also, we adjust SCHED_NR_MIGRATE_BREAK to be aligned with the init value
of sysctl_sched_nr_migrate which can be init to different values.

Then, use SCHED_NR_MIGRATE_BREAK to init sysctl_sched_nr_migrate.

The behavior stays unchanged unless you modify sysctl_sched_nr_migrate
trough debugfs.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/core.c | 6 +-----
kernel/sched/fair.c | 11 ++++-------
kernel/sched/sched.h | 6 ++++++
3 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 64c08993221b..a21e817bdd1c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -142,11 +142,7 @@ __read_mostly int sysctl_resched_latency_warn_once = 1;
* Number of tasks to iterate in a single balance run.
* Limited because this is done with IRQs disabled.
*/
-#ifdef CONFIG_PREEMPT_RT
-const_debug unsigned int sysctl_sched_nr_migrate = 8;
-#else
-const_debug unsigned int sysctl_sched_nr_migrate = 32;
-#endif
+const_debug unsigned int sysctl_sched_nr_migrate = SCHED_NR_MIGRATE_BREAK;

__read_mostly int scheduler_running;

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 02b7b808e186..6972a1a29a48 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8012,8 +8012,6 @@ static struct task_struct *detach_one_task(struct lb_env *env)
return NULL;
}

-static const unsigned int sched_nr_migrate_break = 32;
-
/*
* detach_tasks() -- tries to detach up to imbalance load/util/tasks from
* busiest_rq, as part of a balancing operation within domain "sd".
@@ -8062,7 +8060,7 @@ static int detach_tasks(struct lb_env *env)

/* take a breather every nr_migrate tasks */
if (env->loop > env->loop_break) {
- env->loop_break += sched_nr_migrate_break;
+ env->loop_break += SCHED_NR_MIGRATE_BREAK;
env->flags |= LBF_NEED_BREAK;
break;
}
@@ -10103,14 +10101,13 @@ static int load_balance(int this_cpu, struct rq *this_rq,
struct rq *busiest;
struct rq_flags rf;
struct cpumask *cpus = this_cpu_cpumask_var_ptr(load_balance_mask);
-
struct lb_env env = {
.sd = sd,
.dst_cpu = this_cpu,
.dst_rq = this_rq,
.dst_grpmask = sched_group_span(sd->groups),
.idle = idle,
- .loop_break = sched_nr_migrate_break,
+ .loop_break = SCHED_NR_MIGRATE_BREAK,
.cpus = cpus,
.fbq_type = all,
.tasks = LIST_HEAD_INIT(env.tasks),
@@ -10219,7 +10216,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
env.dst_cpu = env.new_dst_cpu;
env.flags &= ~LBF_DST_PINNED;
env.loop = 0;
- env.loop_break = sched_nr_migrate_break;
+ env.loop_break = SCHED_NR_MIGRATE_BREAK;

/*
* Go back to "more_balance" rather than "redo" since we
@@ -10251,7 +10248,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
*/
if (!cpumask_subset(cpus, env.dst_grpmask)) {
env.loop = 0;
- env.loop_break = sched_nr_migrate_break;
+ env.loop_break = SCHED_NR_MIGRATE_BREAK;
goto redo;
}
goto out_all_pinned;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3ccd35c22f0f..d5cfd1b5bfe9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2423,6 +2423,12 @@ extern void deactivate_task(struct rq *rq, struct task_struct *p, int flags);

extern void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags);

+#ifdef CONFIG_PREEMPT_RT
+#define SCHED_NR_MIGRATE_BREAK 8
+#else
+#define SCHED_NR_MIGRATE_BREAK 32
+#endif
+
extern const_debug unsigned int sysctl_sched_nr_migrate;
extern const_debug unsigned int sysctl_sched_migration_cost;

--
2.17.1