[PATCH v4 06/14] debug: Toggle lazy at runtime and change flush jiffies

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

Enable/Disable this feature by writing 1 or 0 /proc/sys/vm/rcu_lazy.

Change value of /proc/sys/vm/rcu_lazy_jiffies to change max duration before
flush.

Do not merge, only for debug for reviewers.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 include/linux/sched/sysctl.h |  3 +++
 kernel/rcu/tree_nocb.h       |  9 +++++++++
 kernel/sysctl.c              | 17 +++++++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index 2cd928f15df6..54610f9cd962 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -14,6 +14,9 @@ extern unsigned long sysctl_hung_task_timeout_secs;
 enum { sysctl_hung_task_timeout_secs = 0 };
 #endif
 
+extern unsigned int sysctl_rcu_lazy;
+extern unsigned int sysctl_rcu_lazy_jiffies;
+
 enum sched_tunable_scaling {
 	SCHED_TUNABLESCALING_NONE,
 	SCHED_TUNABLESCALING_LOG,
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index edb4e59dbf38..16621b32de46 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -266,6 +266,9 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
 #define LAZY_FLUSH_JIFFIES (10 * HZ)
 unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES;
 
+unsigned int sysctl_rcu_lazy_jiffies = LAZY_FLUSH_JIFFIES;
+unsigned int sysctl_rcu_lazy = 1;
+
 #ifdef CONFIG_RCU_LAZY
 // To be called only from test code.
 void rcu_lazy_set_jiffies_till_flush(unsigned long jif)
@@ -292,6 +295,9 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
 	struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
 	unsigned long mod_jif = 0;
 
+	/* debug: not for merge */
+	rcu_lazy_set_jiffies_till_flush(sysctl_rcu_lazy_jiffies);
+
 	raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
 
 	/*
@@ -697,6 +703,9 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 	unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
 	bool wasempty = false;
 
+	/* debug: not for merge */
+	rcu_lazy_set_jiffies_till_flush(sysctl_rcu_lazy_jiffies);
+
 	/*
 	 * Each pass through the following loop checks for CBs and for the
 	 * nearest grace period (if any) to wait for next.  The CB kthreads
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b00f92df0af5..bbe25d635dc0 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2450,6 +2450,23 @@ static struct ctl_table vm_table[] = {
 		.extra2		= SYSCTL_ONE,
 	},
 #endif
+#ifdef CONFIG_RCU_LAZY
+	{
+		.procname	= "rcu_lazy",
+		.data		= &sysctl_rcu_lazy,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+	{
+		.procname	= "rcu_lazy_jiffies",
+		.data		= &sysctl_rcu_lazy_jiffies,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+#endif
+
 	{ }
 };
 
-- 
2.37.2.609.g9ff673ca1a-goog