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torture: Periodically pause in stutter_wait()

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Running locktorture scenario LOCK05 results in hangs:

tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --torture lock --duration 3 --configs LOCK05

The lock_torture_writer() kthreads set themselves to MAX_NICE while
running SCHED_OTHER.  Other locktorture kthreads run at default niceness,
also SCHED_OTHER.  This results in these other locktorture kthreads
indefinitely preempting the lock_torture_writer() kthreads.  Note that
the cond_resched() in the stutter_wait() function's loop is ineffective
because this scenario is built with CONFIG_PREEMPT=y.

It is not clear that such indefinite preemption is supposed to happen, but
in the meantime this commit prevents kthreads running in stutter_wait()
from being completely CPU-bound, thus allowing the other threads to get
some CPU in a timely fashion.  This commit also uses hrtimers to provide
very short sleeps to avoid degrading the sudden-on testing that stutter
is supposed to provide.

Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-09-01 16:58:41 -07:00
parent 3480d6774f
commit 19012b786e
1 changed files with 14 additions and 2 deletions
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16
kernel/torture.c
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@ -602,8 +602,11 @@ static int stutter_gap;
*/
bool stutter_wait(const char *title)
{
int spt;
ktime_t delay;
unsigned int i = 0;
int oldnice;
bool ret = false;
int spt;
cond_resched_tasks_rcu_qs();
spt = READ_ONCE(stutter_pause_test);
@ -612,8 +615,17 @@ bool stutter_wait(const char *title)
if (spt == 1) {
schedule_timeout_interruptible(1);
} else if (spt == 2) {
while (READ_ONCE(stutter_pause_test))
oldnice = task_nice(current);
set_user_nice(current, MAX_NICE);
while (READ_ONCE(stutter_pause_test)) {
if (!(i++ & 0xffff)) {
set_current_state(TASK_INTERRUPTIBLE);
delay = 10 * NSEC_PER_USEC;
schedule_hrtimeout(&delay, HRTIMER_MODE_REL);
}
cond_resched();
}
set_user_nice(current, oldnice);
} else {
schedule_timeout_interruptible(round_jiffies_relative(HZ));
}