linux-kernel - [PATCH tip/core/rcu 1/3] rcutorture: Occasionally delay readers enough to make RCU force_quiescent

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Date:	Tue,  8 Sep 2009 15:54:35 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josht@...ux.vnet.ibm.com, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Josh Triplett <josh@...htriplett.org>
Subject: [PATCH tip/core/rcu 1/3] rcutorture: Occasionally delay readers enough to make RCU force_quiescent_state

From: Josh Triplett <josh@...htriplett.org>

rcutorture already delays readers, but never for long enough to make RCU
force a quiescent state.  Add an occasional delay of 50ms.

Signed-off-by: Josh Triplett <josh@...htriplett.org>
---
 kernel/rcutorture.c |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index b33db53..328a825 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -281,14 +281,17 @@ static int rcu_torture_read_lock(void) __acquires(RCU)
 
 static void rcu_read_delay(struct rcu_random_state *rrsp)
 {
-	long delay;
-	const long longdelay = 200;
+	const unsigned long shortdelay_us = 200;
+	const unsigned long longdelay_ms = 50;
 
-	/* We want there to be long-running readers, but not all the time. */
+	/* We want a short delay sometimes to make a reader delay the grace
+	 * period, and we want a long delay occasionally to trigger
+	 * force_quiescent_state. */
 
-	delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay);
-	if (!delay)
-		udelay(longdelay);
+	if (!(rcu_random(rrsp) % (nrealreaders * 2000 * longdelay_ms)))
+		mdelay(longdelay_ms);
+	if (!(rcu_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
+		udelay(shortdelay_us);
 }
 
 static void rcu_torture_read_unlock(int idx) __releases(RCU)
-- 
1.5.2.5

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