From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
valentin.schneider@arm.com,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu/urgent 2/2] refscale: Avoid false-positive warnings in ref_scale_reader()
Date: Wed, 14 Jul 2021 13:50:43 -0700 [thread overview]
Message-ID: <20210714205043.2033697-2-paulmck@kernel.org> (raw)
In-Reply-To: <20210714204928.GA2033276@paulmck-ThinkPad-P17-Gen-1>
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 <paulmck@kernel.org>
---
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 313d4547cbc7..d998a76fb542 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))
--
2.31.1.189.g2e36527f23
prev parent reply other threads:[~2021-07-14 20:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-14 20:49 [PATCH rcu/urgent 0/2] Adjust for updated scheduler CPU-affinity semantics Paul E. McKenney
2021-07-14 20:50 ` [PATCH rcu/urgent 1/2] scftorture: Avoid false-positive warnings in scftorture_invoker() Paul E. McKenney
2021-07-14 20:50 ` Paul E. McKenney [this message]
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