sched/debug: Add debugfs knob for "sched_debug"

I'm forever late for editing my kernel cmdline, add a runtime knob to
disable the "sched_debug" thing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170907150614.142924283@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/debug.c

@@ -181,11 +181,16 @@ static const struct file_operations sched_feat_fops = {
 	.release	= single_release,
 };
 
+__read_mostly bool sched_debug_enabled;
+
 static __init int sched_init_debug(void)
 {
 	debugfs_create_file("sched_features", 0644, NULL, NULL,
 			&sched_feat_fops);
 
+	debugfs_create_bool("sched_debug", 0644, NULL,
+			&sched_debug_enabled);
+
 	return 0;
 }
 late_initcall(sched_init_debug);

kernel/sched/sched.h

@@ -1954,6 +1954,8 @@ extern struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq);
 extern struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq);
 
 #ifdef	CONFIG_SCHED_DEBUG
+extern bool sched_debug_enabled;
+
 extern void print_cfs_stats(struct seq_file *m, int cpu);
 extern void print_rt_stats(struct seq_file *m, int cpu);
 extern void print_dl_stats(struct seq_file *m, int cpu);

kernel/sched/topology.c

@@ -14,11 +14,9 @@ cpumask_var_t sched_domains_tmpmask2;
 
 #ifdef CONFIG_SCHED_DEBUG
 
-static __read_mostly int sched_debug_enabled;
-
 static int __init sched_debug_setup(char *str)
 {
-	sched_debug_enabled = 1;
+	sched_debug_enabled = true;
 
 	return 0;
 }