linux-kernel - [PATCH tip/core/rcu 30/45] rcutorture: Make rcu_torture_reader() use cond

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Date:	Mon, 28 Apr 2014 17:25:18 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	oleg@...hat.com, sbw@....edu,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 30/45] rcutorture: Make rcu_torture_reader() use cond_resched()

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

The rcu_torture_reader() function currently uses schedule().  This commit
therefore speeds things up a bit by substituting cond_resched().
This change makes rcu_torture_reader() more CPU-bound, so this commit
also adjusts the number of readers (the "nreaders" module parameter,
which feeds into the "nrealreaders" variable) to allow one CPU to be
free of readers on SMP systems.  The point of this is to increase the
probability that readers will be watching while an updater makes a change.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/rcutorture.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 15af04177e7e..ea8af005ea3f 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -941,7 +941,7 @@ rcu_torture_reader(void *arg)
 		__this_cpu_inc(rcu_torture_batch[completed]);
 		preempt_enable();
 		cur_ops->readunlock(idx);
-		schedule();
+		cond_resched();
 		stutter_wait("rcu_torture_reader");
 	} while (!torture_must_stop());
 	if (irqreader && cur_ops->irq_capable)
@@ -1481,10 +1481,13 @@ rcu_torture_init(void)
 	if (cur_ops->init)
 		cur_ops->init(); /* no "goto unwind" prior to this point!!! */
 
-	if (nreaders >= 0)
+	if (nreaders >= 0) {
 		nrealreaders = nreaders;
-	else
-		nrealreaders = 2 * num_online_cpus();
+	} else {
+		nrealreaders = num_online_cpus() - 1;
+		if (nrealreaders <= 0)
+			nrealreaders = 1;
+	}
 	rcu_torture_print_module_parms(cur_ops, "Start of test");
 
 	/* Set up the freelist. */
-- 
1.8.1.5

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