[PATCH tip/core/rcu 30/47] rcutorture: Permit holding off CPU-hotplug operations during boot

From: Paul E. McKenney
Date: Fri Feb 03 2012 - 20:53:38 EST

From: "Paul E. McKenney" <paul.mckenney@xxxxxxxxxx>

When rcutorture is started automatically at boot time, it might well
also start CPU-hotplug operations at that time, which might not be
desirable. This commit therefore adds an rcutorture parameter that
allows CPU-hotplug operations to be held off for the specified number
of seconds after the start of boot.

Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Documentation/RCU/torture.txt | 13 +++++++++++--
kernel/rcutorture.c | 12 ++++++++++--
2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index d67068d..01a809b 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -69,6 +69,13 @@ onoff_interval
CPU-hotplug operations regardless of what value is
specified for onoff_interval.

+onoff_holdoff The number of seconds to wait until starting CPU-hotplug
+ operations. This would normally only be used when
+ rcutorture was built into the kernel and started
+ automatically at boot time, in which case it is useful
+ in order to avoid confusing boot-time code with CPUs
+ coming and going.
The number of seconds to keep the test threads affinitied
to a particular subset of the CPUs, defaults to 3 seconds.
@@ -277,5 +284,7 @@ The following script may be used to torture RCU:

The output can be manually inspected for the error flag of "!!!".
One could of course create a more elaborate script that automatically
-checked for such errors. The "rmmod" command forces a "SUCCESS" or
-"FAILURE" indication to be printk()ed.
+checked for such errors. The "rmmod" command forces a "SUCCESS",
+"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed. The first
+two are self-explanatory, while the last indicates that while there
+were no RCU failures, CPU-hotplug problems were detected.
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index a94eaef..eeafbd0 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -65,6 +65,7 @@ static int fqs_duration; /* Duration of bursts (us), 0 to disable. */
static int fqs_holdoff; /* Hold time within burst (us). */
static int fqs_stutter = 3; /* Wait time between bursts (s). */
static int onoff_interval; /* Wait time between CPU hotplugs, 0=disable. */
+static int onoff_holdoff; /* Seconds after boot before CPU hotplugs. */
static int shutdown_secs; /* Shutdown time (s). <=0 for no shutdown. */
static int test_boost = 1; /* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */
static int test_boost_interval = 7; /* Interval between boost tests, seconds. */
@@ -95,6 +96,8 @@ module_param(fqs_stutter, int, 0444);
MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
module_param(onoff_interval, int, 0444);
MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable");
+module_param(onoff_holdoff, int, 0444);
+MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)");
module_param(shutdown_secs, int, 0444);
MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), zero to disable.");
module_param(test_boost, int, 0444);
@@ -1300,13 +1303,13 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag)
"fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d "
"test_boost=%d/%d test_boost_interval=%d "
"test_boost_duration=%d shutdown_secs=%d "
- "onoff_interval=%d\n",
+ "onoff_interval=%d onoff_holdoff=%d\n",
torture_type, tag, nrealreaders, nfakewriters,
stat_interval, verbose, test_no_idle_hz, shuffle_interval,
stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
test_boost, cur_ops->can_boost,
test_boost_interval, test_boost_duration, shutdown_secs,
- onoff_interval);
+ onoff_interval, onoff_holdoff);

static struct notifier_block rcutorture_shutdown_nb = {
@@ -1410,6 +1413,11 @@ rcu_torture_onoff(void *arg)
maxcpu = cpu;
WARN_ON(maxcpu < 0);
+ if (onoff_holdoff > 0) {
+ VERBOSE_PRINTK_STRING("rcu_torture_onoff begin holdoff");
+ schedule_timeout_interruptible(onoff_holdoff * HZ);
+ VERBOSE_PRINTK_STRING("rcu_torture_onoff end holdoff");
+ }
while (!kthread_should_stop()) {
cpu = (rcu_random(&rand) >> 4) % (maxcpu + 1);
if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) {

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