linux-kernel - [PATCH tip/core/rcu 3/4] rcu: Run rcuo kthreads at elevated priority in CONFIG_RCU

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Date:   Tue, 19 Jan 2021 20:32:35 -0800
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.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>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Scott Wood <swood@...hat.com>
Subject: [PATCH tip/core/rcu 3/4] rcu: Run rcuo kthreads at elevated priority in CONFIG_RCU_BOOST kernels

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

The priority level of the rcuo kthreads is the system administrator's
responsibility, but kernels that priority-boost RCU readers probably need
the rcuo kthreads running at the rcutree.kthread_prio level.  This commit
therefore sets these kthreads to that priority level at creation time,
providing a sensible default.  The system administrator is free to adjust
as needed at any time.

Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Scott Wood <swood@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree_plugin.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index fca31c6..7e33dae0 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2197,6 +2197,7 @@ static int rcu_nocb_gp_kthread(void *arg)
 {
 	struct rcu_data *rdp = arg;
 
+	rcu_cpu_kthread_setup(-1);
 	for (;;) {
 		WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
 		nocb_gp_wait(rdp);
@@ -2298,6 +2299,7 @@ static int rcu_nocb_cb_kthread(void *arg)
 
 	// Each pass through this loop does one callback batch, and,
 	// if there are no more ready callbacks, waits for them.
+	rcu_cpu_kthread_setup(-1);
 	for (;;) {
 		nocb_cb_wait(rdp);
 		cond_resched_tasks_rcu_qs();
-- 
2.9.5