linux-kernel - [PATCH 13/22] x86: smp: move cpumask_weight() out of for-loop in remove

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Date:   Tue, 10 May 2022 08:47:41 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Laight <David.Laight@...LAB.COM>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joe Perches <joe@...ches.com>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Nicholas Piggin <npiggin@...il.com>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Peter Zijlstra <peterz@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Balbir Singh <sblbir@...zon.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>, Huang Rui <ray.huang@....com>,
        Ingo Molnar <mingo@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>, x86@...nel.org
Subject: [PATCH 13/22] x86: smp: move cpumask_weight() out of for-loop in remove_siblinginfo

Because argument of the function is constant inside for_each_cpu()
loop, the cpumask_weight() does the same work O(NR_CPUS) times, while
it may be calculated only once.

This patch moves cpumask_weight() out of the loop and replaces it
with cpumask_weight_eq(). While here, fix comment format.

CC: Balbir Singh <sblbir@...zon.com>
CC: Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC: Borislav Petkov <bp@...en8.de>
CC: Dave Hansen <dave.hansen@...ux.intel.com>
CC: H. Peter Anvin <hpa@...or.com>
CC: Huang Rui <ray.huang@....com>
CC: Ingo Molnar <mingo@...hat.com>
CC: Paul E. McKenney <paulmck@...nel.org>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
CC: Sean Christopherson <seanjc@...gle.com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Tim Chen <tim.c.chen@...ux.intel.com>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 arch/x86/kernel/smpboot.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 5e7f9532a10d..7d948f79ef31 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1605,13 +1605,14 @@ static void remove_siblinginfo(int cpu)
 {
 	int sibling;
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
+	bool last_thread_sibling = cpumask_weight_eq(topology_sibling_cpumask(cpu), 1);
 
 	for_each_cpu(sibling, topology_core_cpumask(cpu)) {
 		cpumask_clear_cpu(cpu, topology_core_cpumask(sibling));
-		/*/
+		/*
 		 * last thread sibling in this cpu core going down
 		 */
-		if (cpumask_weight(topology_sibling_cpumask(cpu)) == 1)
+		if (last_thread_sibling)
 			cpu_data(sibling).booted_cores--;
 	}
 
-- 
2.32.0