sched/fair: Cleanup loop_max and loop_break

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220825122726.20819-3-vincent.guittot@linaro.org

Author: vingu-linaro

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;
 

kernel/sched/fair.c

@@ -8009,8 +8009,6 @@ 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".
@@ -8059,7 +8057,7 @@ 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;
 		}
@@ -10100,14 +10098,13 @@ 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),
@@ -10216,7 +10213,7 @@ 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
@@ -10248,7 +10245,7 @@ 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;

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;