linux-kernel - [PATCH 3/6] driver core: cpu: optimize print_cpus

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Date: Mon, 13 May 2024 15:01:43 -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 3/6] driver core: cpu: optimize print_cpus_isolated()

The function may be called with housekeeping_cpumask == cpu_possible_mask,
and in such case the 'isolated' cpumask would be just empty.

We can call cpumask_clear() in that case, and save CPU cycles.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 drivers/base/cpu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 56fba44ba391..1322957286dd 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -282,8 +282,10 @@ static ssize_t print_cpus_isolated(struct device *dev,
 	if (!alloc_cpumask_var(&isolated, GFP_KERNEL))
 		return -ENOMEM;
 
-	cpumask_andnot(isolated, cpu_possible_mask,
-		       housekeeping_cpumask(HK_TYPE_DOMAIN));
+	if (cpu_possible_mask != housekeeping_cpumask(HK_TYPE_DOMAIN))
+		cpumask_andnot(isolated, cpu_possible_mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
+	else
+		cpumask_clear(isolated);
 	len = sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(isolated));
 
 	free_cpumask_var(isolated);
-- 
2.40.1