linux-kernel - [PATCH tip/core/rcu 19/30] refperf: Simplify initialization-time wakeup protocol

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Message-Id: <20200623003013.26252-19-paulmck@kernel.org>
Date:   Mon, 22 Jun 2020 17:30:02 -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 19/30] refperf: Simplify initialization-time wakeup protocol

From: "Paul E. McKenney" <paulmck@...nel.org>

This commit moves the reader-launch wait loop from ref_perf_init()
to main_func(), removing one layer of wakeup and allowing slightly
faster system boot.

Cc: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/refperf.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/refperf.c b/kernel/rcu/refperf.c
index 2d2d227..7839237 100644
--- a/kernel/rcu/refperf.c
+++ b/kernel/rcu/refperf.c
@@ -369,13 +369,14 @@ static int main_func(void *arg)
 		VERBOSE_PERFOUT_ERRSTRING("out of memory");
 		errexit = true;
 	}
-	atomic_inc(&n_init);
-
-	// Wait for all threads to start.
-	wait_event(main_wq, atomic_read(&n_init) == (nreaders + 1));
 	if (holdoff)
 		schedule_timeout_interruptible(holdoff * HZ);
 
+	// Wait for all threads to start.
+	atomic_inc(&n_init);
+	while (atomic_read(&n_init) < nreaders + 1)
+		schedule_timeout_uninterruptible(1);
+
 	// Start exp readers up per experiment
 	for (exp = 0; exp < nruns && !torture_must_stop(); exp++) {
 		if (errexit)
@@ -565,14 +566,6 @@ ref_perf_init(void)
 	firsterr = torture_create_kthread(main_func, NULL, main_task);
 	if (firsterr)
 		goto unwind;
-	schedule_timeout_uninterruptible(1);
-
-
-	// Wait until all threads start
-	while (atomic_read(&n_init) < nreaders + 1)
-		schedule_timeout_uninterruptible(1);
-
-	wake_up(&main_wq);
 
 	torture_init_end();
 	return 0;
-- 
2.9.5