sched/debug: Make sysrq prints of sched debug data optional

Calls to sysrq_sched_debug_show() can yield rather verbose output
which contributes to log spew and, under heavy load, may increase
the chances of a watchdog bark.

Make printing of this data optional with the introduction of a
new Kconfig, CONFIG_SYSRQ_SCHED_DEBUG.

Change-Id: I5f54d901d0dea403109f7ac33b8881d967a899ed
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>

kernel/sched/core.c

@@ -4931,7 +4931,7 @@ void show_state_filter(unsigned long state_filter)
 
 	touch_all_softlockup_watchdogs();
 
-#ifdef CONFIG_SCHED_DEBUG
+#ifdef CONFIG_SYSRQ_SCHED_DEBUG
 	sysrq_sched_debug_show();
 #endif
 	rcu_read_unlock();

kernel/sched/debug.c

@@ -374,10 +374,12 @@ static int sched_debug_show(struct seq_file *m, void *v)
 	return 0;
 }
 
+#ifdef CONFIG_SYSRQ_SCHED_DEBUG
 void sysrq_sched_debug_show(void)
 {
 	sched_debug_show(NULL, NULL);
 }
+#endif
 
 static int sched_debug_open(struct inode *inode, struct file *filp)
 {

kernel/sched/sched.h

@@ -872,7 +872,9 @@ static inline void idle_balance(int cpu, struct rq *rq)
 
 #endif
 
+#ifdef CONFIG_SYSRQ_SCHED_DEBUG
 extern void sysrq_sched_debug_show(void);
+#endif
 extern void sched_init_granularity(void);
 extern void update_max_interval(void);
 extern void update_group_power(struct sched_domain *sd, int cpu);

lib/Kconfig.debug

@@ -291,6 +291,15 @@ config SCHED_DEBUG
 	  that can help debug the scheduler. The runtime overhead of this
 	  option is minimal.
 
+config SYSRQ_SCHED_DEBUG
+	bool "Print scheduling debugging info from sysrq-trigger"
+	depends on SCHED_DEBUG
+	default y
+	help
+	  If you say Y here, the "show-task-states(T)" and
+	  "show-blocked-tasks(W)" sysrq-triggers will print additional
+	  scheduling statistics.
+
 config SCHEDSTATS
 	bool "Collect scheduler statistics"
 	depends on DEBUG_KERNEL && PROC_FS