linux-kernel - [PATCH rcu 04/14] rcu: Eliminate rcu_implicit_dynticks

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Date:   Wed, 15 Sep 2021 16:33:33 -0700
From:   "Paul E. McKenney" <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>
Subject: [PATCH rcu 04/14] rcu: Eliminate rcu_implicit_dynticks_qs() local variable ruqp

The rcu_implicit_dynticks_qs() function's local variable ruqp references
the ->rcu_urgent_qs field in the rcu_data structure referenced by the
function parameter rdp, with a rather odd method for computing the
pointer to this field.  This commit therefore simplifies things and
saves a couple of lines of code by replacing each instance of ruqp with
&rdp->need_heavy_qs.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 18d2f35d1450..0bfebec94277 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1219,7 +1219,6 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 {
 	unsigned long jtsq;
-	bool *ruqp;
 	struct rcu_node *rnp = rdp->mynode;
 
 	/*
@@ -1284,16 +1283,15 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	 * is set way high.
 	 */
 	jtsq = READ_ONCE(jiffies_to_sched_qs);
-	ruqp = per_cpu_ptr(&rcu_data.rcu_urgent_qs, rdp->cpu);
 	if (!READ_ONCE(rdp->rcu_need_heavy_qs) &&
 	    (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
 	     time_after(jiffies, rcu_state.jiffies_resched) ||
 	     rcu_state.cbovld)) {
 		WRITE_ONCE(rdp->rcu_need_heavy_qs, true);
 		/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
-		smp_store_release(ruqp, true);
+		smp_store_release(&rdp->rcu_urgent_qs, true);
 	} else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
-		WRITE_ONCE(*ruqp, true);
+		WRITE_ONCE(rdp->rcu_urgent_qs, true);
 	}
 
 	/*
@@ -1307,7 +1305,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	if (tick_nohz_full_cpu(rdp->cpu) &&
 	    (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
 	     rcu_state.cbovld)) {
-		WRITE_ONCE(*ruqp, true);
+		WRITE_ONCE(rdp->rcu_urgent_qs, true);
 		resched_cpu(rdp->cpu);
 		WRITE_ONCE(rdp->last_fqs_resched, jiffies);
 	}
-- 
2.31.1.189.g2e36527f23