Commit 05bc276c authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

refscale: Avoid false-positive warnings in ref_scale_reader() 



If the call to set_cpus_allowed_ptr() in ref_scale_reader()
fails, a later WARN_ONCE() complains.  But with the advent of
570a752b ("lib/smp_processor_id: Use is_percpu_thread() instead of
nr_cpus_allowed"), this complaint can be drowned out by complaints from
smp_processor_id().  The rationale for this change is that refscale's
kthreads are not marked with PF_NO_SETAFFINITY, which means that a system
administrator could change affinity at any time.

However, refscale is a performance/stress test, and the system
administrator might well have a valid test-the-test reason for changing
affinity.  This commit therefore changes to raw_smp_processor_id()
in order to avoid the noise, and also adds a WARN_ON_ONCE() to the
call to set_cpus_allowed_ptr() in order to directly detect immediate
failure.  There is no WARN_ON_ONCE() within the test loop, allowing
human-reflex-based affinity resetting, if desired.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 22b6d149

kernel/rcu/refscale.c

+3 −3
Original line number Diff line number Diff line
@@ -487,13 +487,13 @@ ref_scale_reader(void *arg) 
	s64 duration;



	VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: task started", me);

	set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));

	WARN_ON_ONCE(set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)));

	set_user_nice(current, MAX_NICE);

	atomic_inc(&n_init);

	if (holdoff)

		schedule_timeout_interruptible(holdoff * HZ);

repeat:

	VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id());

	VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, raw_smp_processor_id());



	// Wait for signal that this reader can start.

	wait_event(rt->wq, (atomic_read(&nreaders_exp) && smp_load_acquire(&rt->start_reader)) ||
@@ -503,7 +503,7 @@ ref_scale_reader(void *arg) 
		goto end;



	// Make sure that the CPU is affinitized appropriately during testing.

	WARN_ON_ONCE(smp_processor_id() != me);

	WARN_ON_ONCE(raw_smp_processor_id() != me);



	WRITE_ONCE(rt->start_reader, 0);

	if (!atomic_dec_return(&n_started))