From 05bc276cf243d90b9f1eb6ae2962f41eeb53a741 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 10 Jun 2021 09:24:43 -0700 Subject: [PATCH] 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 570a752b7a9b ("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: Paul E. McKenney --- kernel/rcu/refscale.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c index 313d4547cbc7bf..d998a76fb5422e 100644 --- a/kernel/rcu/refscale.c +++ b/kernel/rcu/refscale.c @@ -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))