linux-kernel - [PATCH rcu 6/9] rcu-tasks: Restore use of timers for non-RT kernels

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Message-Id: <20220419000014.3948512-6-paulmck@kernel.org>
Date:   Mon, 18 Apr 2022 17:00:11 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 6/9] rcu-tasks: Restore use of timers for non-RT kernels

The use of hrtimers for RCU-tasks grace-period delays works well in
general, but can result in excessive grace-period delays for some
corner-case workloads.  This commit therefore reverts to the use of
timers for non-RT kernels to mitigate those grace-period delays.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tasks.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 71fe340ab82a..405614039515 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -654,9 +654,13 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
 
 		// Slowly back off waiting for holdouts
 		set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS);
-		exp = jiffies_to_nsecs(fract);
-		__set_current_state(TASK_IDLE);
-		schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD);
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+			schedule_timeout_idle(fract);
+		} else {
+			exp = jiffies_to_nsecs(fract);
+			__set_current_state(TASK_IDLE);
+			schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD);
+		}
 
 		if (fract < HZ)
 			fract++;
-- 
2.31.1.189.g2e36527f23