linux-kernel - [PATCH] mips: micro-optimize calculate_cpu_foreign

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Message-Id: <20220621144729.533026-1-yury.norov@gmail.com>
Date:   Tue, 21 Jun 2022 07:47:29 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Alexander Lobakin <alobakin@...me>,
        Huacai Chen <chenhuacai@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Mao Bibo <maobibo@...ngson.cn>,
        Philippe Mathieu-Daudé <f4bug@...at.org>,
        WANG Xuerui <kernel@...0n.name>, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>
Subject: [PATCH] mips: micro-optimize calculate_cpu_foreign_map()

The inner loop in calculate_cpu_foreign_map() walks the whole
cpumask to check if we have siblings for a given cpu.

We can just break after a 1st match and avoid useless traversing
the rest of mask.

Loongarch has an identical function, so fix it here as well.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---

It looks like loongarch copied quite a lot from arch/mips/kernel/smp.c.
For loongarch folks: Guys, can you consider moving shared code into a
shared file(s)?

 arch/loongarch/kernel/smp.c | 7 +++----
 arch/mips/kernel/smp.c      | 7 +++----
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
index b8c53b755a25..c1c91df3c8ac 100644
--- a/arch/loongarch/kernel/smp.c
+++ b/arch/loongarch/kernel/smp.c
@@ -463,17 +463,16 @@ static inline void set_cpu_core_map(int cpu)
  */
 void calculate_cpu_foreign_map(void)
 {
-	int i, k, core_present;
+	int i, k;
 	cpumask_t temp_foreign_map;
 
 	/* Re-calculate the mask */
 	cpumask_clear(&temp_foreign_map);
 	for_each_online_cpu(i) {
-		core_present = 0;
 		for_each_cpu(k, &temp_foreign_map)
 			if (cpus_are_siblings(i, k))
-				core_present = 1;
-		if (!core_present)
+				break;
+		if (k >= nr_cpu_ids)
 			cpumask_set_cpu(i, &temp_foreign_map);
 	}
 
diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 1d93b85271ba..a2ce641f5f18 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -115,17 +115,16 @@ static inline void set_cpu_core_map(int cpu)
  */
 void calculate_cpu_foreign_map(void)
 {
-	int i, k, core_present;
+	int i, k;
 	cpumask_t temp_foreign_map;
 
 	/* Re-calculate the mask */
 	cpumask_clear(&temp_foreign_map);
 	for_each_online_cpu(i) {
-		core_present = 0;
 		for_each_cpu(k, &temp_foreign_map)
 			if (cpus_are_siblings(i, k))
-				core_present = 1;
-		if (!core_present)
+				break;
+		if (k >= nr_cpu_ids)
 			cpumask_set_cpu(i, &temp_foreign_map);
 	}
 
-- 
2.32.0