[PATCH 6/7] rcutorture: Add support to get the number of wakeups of main GP kthread

["Joel Fernandes (Google)" <joel@joelfernandes.org>]

This is useful to check for any improvements or degradation related to
number of GP kthread wakeups during testing.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/rcu/Kconfig.debug |  1 +
 kernel/rcu/rcu.h         |  2 ++
 kernel/rcu/rcutorture.c  | 23 ++++++++++++++++++++++-
 kernel/rcu/tree.c        |  7 +++++++
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 3cf6132a4bb9f..3323e3378af5a 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -50,6 +50,7 @@ config RCU_TORTURE_TEST
 	select TASKS_RCU
 	select TASKS_RUDE_RCU
 	select TASKS_TRACE_RCU
+	select SCHEDSTATS
 	default n
 	help
 	  This option provides a kernel module that runs torture tests
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index cf66a3ccd7573..7e867e81d9738 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -511,6 +511,7 @@ srcu_batches_completed(struct srcu_struct *sp) { return 0; }
 static inline void rcu_force_quiescent_state(void) { }
 static inline void show_rcu_gp_kthreads(void) { }
 static inline int rcu_get_gp_kthreads_prio(void) { return 0; }
+static inline struct task_struct *rcu_get_main_gp_kthread(void) { return 0; }
 static inline void rcu_fwd_progress_check(unsigned long j) { }
 #else /* #ifdef CONFIG_TINY_RCU */
 bool rcu_dynticks_zero_in_eqs(int cpu, int *vp);
@@ -519,6 +520,7 @@ unsigned long rcu_exp_batches_completed(void);
 unsigned long srcu_batches_completed(struct srcu_struct *sp);
 void show_rcu_gp_kthreads(void);
 int rcu_get_gp_kthreads_prio(void);
+struct task_struct *rcu_get_main_gp_kthread(void);
 void rcu_fwd_progress_check(unsigned long j);
 void rcu_force_quiescent_state(void);
 extern struct workqueue_struct *rcu_gp_wq;
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index d0d265304d147..959a1f84d6904 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -23,6 +23,7 @@
 #include <linux/rcupdate_wait.h>
 #include <linux/interrupt.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/stat.h>
 #include <uapi/linux/sched/types.h>
 #include <linux/atomic.h>
 #include <linux/bitops.h>
@@ -460,9 +461,29 @@ static void rcu_sync_torture_init(void)
 	INIT_LIST_HEAD(&rcu_torture_removed);
 }
 
+unsigned long rcu_gp_nr_wakeups;
+
+static void rcu_flavor_init(void)
+{
+	rcu_sync_torture_init();
+
+	/* Make sure schedstat is enabled for GP thread wakeup count. */
+	force_schedstat_enabled();
+	rcu_gp_nr_wakeups = rcu_get_main_gp_kthread()->se.statistics.nr_wakeups;
+}
+
+static void rcu_flavor_cleanup(void)
+{
+	unsigned long now_nr = rcu_get_main_gp_kthread()->se.statistics.nr_wakeups;
+
+	pr_alert("End-test: Cleanup: Total GP-kthread wakeups: %lu\n",
+		now_nr - rcu_gp_nr_wakeups);
+}
+
 static struct rcu_torture_ops rcu_ops = {
 	.ttype		= RCU_FLAVOR,
-	.init		= rcu_sync_torture_init,
+	.init		= rcu_flavor_init,
+	.cleanup	= rcu_flavor_cleanup,
 	.readlock	= rcu_torture_read_lock,
 	.read_delay	= rcu_read_delay,
 	.readunlock	= rcu_torture_read_unlock,
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c3bae7a83d792..a3a175feb310a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -175,6 +175,13 @@ int rcu_get_gp_kthreads_prio(void)
 }
 EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
 
+/* Retrieve RCU's main GP kthread task_struct */
+struct task_struct *rcu_get_main_gp_kthread(void)
+{
+	return rcu_state.gp_kthread;
+}
+EXPORT_SYMBOL_GPL(rcu_get_main_gp_kthread);
+
 /*
  * Number of grace periods between delays, normalized by the duration of
  * the delay.  The longer the delay, the more the grace periods between
-- 
2.27.0.111.gc72c7da667-goog