[PATCH tip/core/rcu 02/17] rcutorture: Force occasional reader waits

[Paul E. McKenney]

Deferred quiescent states can interact with the scheduler, but
rcu_torture_reader() does not force such interaction all that frequently.
This commit therefore blocks for one jiffy after ten jiffies of read-side
runtime.  This has the beneficial effect of being most likely to block
just after long-running readers, and it is exactly these readers that
are most likely to have been preempted (in CONFIG_PREEMPT=y kernels).
This in turn helps increase the probability that a deferred quiescent
state will be seen by RCU's context-switch hooks.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcu/rcutorture.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index c596c6f1e457..50a4f0ed4ebf 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1387,6 +1387,7 @@ static void rcu_torture_timer(struct timer_list *unused)
 static int
 rcu_torture_reader(void *arg)
 {
+	unsigned long lastsleep = jiffies;
 	DEFINE_TORTURE_RANDOM(rand);
 	struct timer_list t;
 
@@ -1402,6 +1403,10 @@ rcu_torture_reader(void *arg)
 		}
 		if (!rcu_torture_one_read(&rand))
 			schedule_timeout_interruptible(HZ);
+		if (time_after(jiffies, lastsleep)) {
+			schedule_timeout_interruptible(1);
+			lastsleep = jiffies + 10;
+		}
 		stutter_wait("rcu_torture_reader");
 	} while (!torture_must_stop());
 	if (irqreader && cur_ops->irq_capable) {
-- 
2.17.1