From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.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,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 13/30] refperf: Tune reader measurement interval
Date: Mon, 22 Jun 2020 17:29:56 -0700 [thread overview]
Message-ID: <20200623003013.26252-13-paulmck@kernel.org> (raw)
In-Reply-To: <20200623002941.GA26089@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.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@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.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
next prev parent reply other threads:[~2020-06-23 0:30 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 0:29 [PATCH tip/core/rcu 0/30] Add read-side scalability tests for v5.9 Paul E. McKenney
2020-06-23 0:29 ` [PATCH tip/core/rcu 01/30] rcuperf: Remove useless while loops around wait_event paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 02/30] refperf: Add a test to measure performance of read-side synchronization paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 03/30] rcuperf: Add comments explaining the high reader overhead paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 04/30] torture: Add refperf to the rcutorture scripting paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 05/30] refperf: Add holdoff parameter to allow CPUs to come online paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 06/30] refperf: Hoist function-pointer calls out of the loop paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 07/30] refperf: Allow decimal nanoseconds paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 08/30] refperf: Convert nreaders to a module parameter paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 09/30] refperf: Provide module parameter to specify number of experiments paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 10/30] refperf: Dynamically allocate experiment-summary output buffer paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 11/30] refperf: Dynamically allocate thread-summary " paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 12/30] refperf: Make functions static paulmck
2020-06-23 0:29 ` paulmck [this message]
2020-06-23 0:29 ` [PATCH tip/core/rcu 14/30] refperf: Convert reader_task structure's "start" field to int paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 15/30] refperf: More closely synchronize reader start times paulmck
2020-06-23 0:29 ` [PATCH tip/core/rcu 16/30] refperf: Add warmup and cooldown processing phases paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 17/30] refperf: Label experiment-number column "Runs" paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 18/30] refperf: Output per-experiment data points paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 19/30] refperf: Simplify initialization-time wakeup protocol paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 20/30] refperf: Add read-side delay module parameter paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 21/30] refperf: Adjust refperf.loop default value paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 22/30] doc: Document rcuperf's module parameters paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 23/30] refperf: Work around 64-bit division paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 24/30] refperf: Change readdelay module parameter to nanoseconds paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 25/30] refperf: Add test for RCU Tasks Trace readers paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 26/30] refperf: Add test for RCU Tasks readers paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 27/30] rcu-tasks: Fix synchronize_rcu_tasks_trace() header comment paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 28/30] refperf: Rename RCU_REF_PERF_TEST to RCU_REF_SCALE_TEST paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 29/30] refperf: Rename refperf.c to refscale.c and change internal names paulmck
2020-06-23 0:30 ` [PATCH tip/core/rcu 30/30] refscale: Change --torture type from refperf to refscale paulmck
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