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From: Yury Norov <yury.norov@gmail.com>
To: linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
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	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Imran Khan <imran.f.khan@oracle.com>,
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	Juri Lelli <juri.lelli@redhat.com>,
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	Valentin Schneider <vschneid@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Waiman Long <longman@redhat.com>,
	Yury Norov <yury.norov@gmail.com>,
	Zefan Li <lizefan.x@bytedance.com>,
	cgroups@vger.kernel.org
Subject: [PATCH 3/6] driver core: cpu: optimize print_cpus_isolated()
Date: Mon, 13 May 2024 15:01:43 -0700
Message-Id: <20240513220146.1461457-4-yury.norov@gmail.com>
In-Reply-To: <20240513220146.1461457-1-yury.norov@gmail.com>
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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@gmail.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