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

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Date:   Thu, 18 Jun 2020 16:29:54 -0400
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: [PATCH 6/7] rcutorture: Add support to get the number of wakeups of main GP kthread

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@...lfernandes.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