linux-kernel - [PATCH 3/4] lib/group_cpus: optimize inner loop in grp_spread_init

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Date:   Wed,  1 Nov 2023 15:58:19 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH 3/4] lib/group_cpus: optimize inner loop in grp_spread_init_one()

The loop starts from the beginning every time we switch to the next
sibling mask. This is the Schlemiel the Painter's style of coding
because we know for sure that nmsk is clear up to current CPU, and we
can just continue from the next CPU.

Also, we can do it nicer if leverage the dedicated for_each() iterator.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 lib/group_cpus.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index b1e7d9cc9da9..8afe0c71d204 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -30,13 +30,13 @@ static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
 
 		/* If the cpu has siblings, use them first */
 		siblmsk = topology_sibling_cpumask(cpu);
-		for (sibl = -1; cpus_per_grp > 0; ) {
-			sibl = cpumask_next(sibl, siblmsk);
-			if (sibl >= nr_cpu_ids)
-				break;
+		sibl = cpu + 1;
+
+		for_each_cpu_and_from(sibl, siblmsk, nmsk) {
 			__cpumask_clear_cpu(sibl, nmsk);
 			__cpumask_set_cpu(sibl, irqmsk);
-			cpus_per_grp--;
+			if (cpus_per_grp-- == 0)
+				return;
 		}
 	}
 }
-- 
2.39.2