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Message-Id: <20200623003013.26252-13-paulmck@kernel.org>
Date: Mon, 22 Jun 2020 17:29:56 -0700
From: paulmck@...nel.org
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH tip/core/rcu 13/30] refperf: Tune reader measurement interval
From: "Paul E. McKenney" <paulmck@...nel.org>
This commit moves a printk() out of the measurement interval, converts
a atomic_dec()/atomic_read() pair to atomic_dec_and_test(), and adds
a smp_mb__before_atomic() to avoid potential wake/wait hangs. These
changes have the added benefit of reducing the number of loops required
for amortizing loop overhead for CONFIG_PREEMPT=n RCU measurements from
1,000,000 to 10,000. This reduction in turn shortens the test, reducing
the probability of interference.
Cc: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
kernel/rcu/refperf.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/rcu/refperf.c b/kernel/rcu/refperf.c
index 0a900f3..8815ccf 100644
--- a/kernel/rcu/refperf.c
+++ b/kernel/rcu/refperf.c
@@ -252,15 +252,16 @@ ref_perf_reader(void *arg)
// Make sure that the CPU is affinitized appropriately during testing.
WARN_ON_ONCE(smp_processor_id() != me);
+ smp_mb__before_atomic();
atomic_dec(&rt->start);
+ VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d started", me, exp_idx);
+
// To prevent noise, keep interrupts disabled. This also has the
// effect of preventing entries into slow path for rcu_read_unlock().
local_irq_save(flags);
start = ktime_get_mono_fast_ns();
- VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d started", me, exp_idx);
-
cur_ops->readsection(loops);
duration = ktime_get_mono_fast_ns() - start;
@@ -268,14 +269,12 @@ ref_perf_reader(void *arg)
rt->last_duration_ns = WARN_ON_ONCE(duration < 0) ? 0 : duration;
- atomic_dec(&nreaders_exp);
+ if (atomic_dec_and_test(&nreaders_exp))
+ wake_up(&main_wq);
VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d ended, (readers remaining=%d)",
me, exp_idx, atomic_read(&nreaders_exp));
- if (!atomic_read(&nreaders_exp))
- wake_up(&main_wq);
-
if (!torture_must_stop())
goto repeat;
end:
--
2.9.5
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