linux-kernel - [PATCH 07/12] rcutorture: Comment invocations of tick_dep_set

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Message-ID: <20250418161005.2425391-22-joelagnelf@nvidia.com>
Date: Fri, 18 Apr 2025 12:09:53 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: linux-kernel@...r.kernel.org,
	Davidlohr Bueso <dave@...olabs.net>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Cc: rcu@...r.kernel.org,
	Joel Fernandes <joelagnelf@...dia.com>
Subject: [PATCH 07/12] rcutorture: Comment invocations of tick_dep_set_task()

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

The rcu_torture_reader() and rcu_torture_fwd_prog_cr() functions
run CPU-bound for extended periods of time (tens or even
hundreds of milliseconds), so they invoke tick_dep_set_task() and
tick_dep_clear_task() to ensure that the scheduling-clock tick helps
move grace periods forward.

So why doesn't rcu_torture_fwd_prog_nr() also invoke tick_dep_set_task()
and tick_dep_clear_task()?  Because the point of this function is to test
RCU's ability to (eventually) force grace periods forward even when the
tick has been disabled during long CPU-bound kernel execution.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
---
 kernel/rcu/rcutorture.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7eccc74e60a7..ea40f3ad32dc 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2410,7 +2410,7 @@ rcu_torture_reader(void *arg)
 	set_user_nice(current, MAX_NICE);
 	if (irqreader && cur_ops->irq_capable)
 		timer_setup_on_stack(&t, rcu_torture_timer, 0);
-	tick_dep_set_task(current, TICK_DEP_BIT_RCU);
+	tick_dep_set_task(current, TICK_DEP_BIT_RCU);  // CPU bound, so need tick.
 	do {
 		if (irqreader && cur_ops->irq_capable) {
 			if (!timer_pending(&t))
@@ -3260,7 +3260,7 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp)
 	cver = READ_ONCE(rcu_torture_current_version);
 	gps = cur_ops->get_gp_seq();
 	rfp->rcu_launder_gp_seq_start = gps;
-	tick_dep_set_task(current, TICK_DEP_BIT_RCU);
+	tick_dep_set_task(current, TICK_DEP_BIT_RCU);  // CPU bound, so need tick.
 	while (time_before(jiffies, stopat) &&
 	       !shutdown_time_arrived() &&
 	       !READ_ONCE(rcu_fwd_emergency_stop) && !torture_must_stop()) {
-- 
2.43.0