linux-kernel - [PATCH 6/6] tick/common: optimize cpumask

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Date: Mon, 13 May 2024 15:01:46 -0700
From: Yury Norov <yury.norov@...il.com>
To: linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Ben Segall <bsegall@...gle.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Imran Khan <imran.f.khan@...cle.com>,
	Ingo Molnar <mingo@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Leonardo Bras <leobras@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...riel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Waiman Long <longman@...hat.com>,
	Yury Norov <yury.norov@...il.com>,
	Zefan Li <lizefan.x@...edance.com>,
	cgroups@...r.kernel.org
Subject: [PATCH 6/6] tick/common: optimize cpumask_equal() usage

Some functions in the file call cpumask_equal() with src1p == src2p.
We can obviously just skip comparison entirely in this case.

This patch fixes cpumask_equal invocations when boot-test or LTP detect
such condition.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 kernel/time/tick-common.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index d88b13076b79..b31fef292833 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -253,7 +253,8 @@ static void tick_setup_device(struct tick_device *td,
 	 * When the device is not per cpu, pin the interrupt to the
 	 * current cpu:
 	 */
-	if (!cpumask_equal(newdev->cpumask, cpumask))
+	if (newdev->cpumask != cpumask &&
+			!cpumask_equal(newdev->cpumask, cpumask))
 		irq_set_affinity(newdev->irq, cpumask);
 
 	/*
@@ -288,14 +289,19 @@ static bool tick_check_percpu(struct clock_event_device *curdev,
 {
 	if (!cpumask_test_cpu(cpu, newdev->cpumask))
 		return false;
-	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
+	if (newdev->cpumask == cpumask_of(cpu) ||
+			cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
 		return true;
 	/* Check if irq affinity can be set */
 	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
 		return false;
 	/* Prefer an existing cpu local device */
-	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
+	if (!curdev)
+		return true;
+	if (curdev->cpumask == cpumask_of(cpu) ||
+			cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
 		return false;
+
 	return true;
 }
 
@@ -316,7 +322,8 @@ static bool tick_check_preferred(struct clock_event_device *curdev,
 	 */
 	return !curdev ||
 		newdev->rating > curdev->rating ||
-	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
+		!(curdev->cpumask == newdev->cpumask &&
+			cpumask_equal(curdev->cpumask, newdev->cpumask));
 }
 
 /*
-- 
2.40.1