linux-kernel - [PATCH 2/9] lib/group_cpus: optimize inner loop in grp_spread_init

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Date: Fri, 19 Jan 2024 18:50:46 -0800
From: Yury Norov <yury.norov@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ming Lei <ming.lei@...hat.com>,
	linux-kernel@...r.kernel.org
Cc: Yury Norov <yury.norov@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Breno Leitao <leitao@...ian.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Zi Yan <ziy@...dia.com>
Subject: [PATCH 2/9] 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,
and simplify the logic of clearing a bit in nmsk.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 lib/group_cpus.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index ee272c4cefcc..063ed9ae1b8d 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -30,14 +30,14 @@ 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;
-			if (!cpumask_test_and_clear_cpu(sibl, nmsk))
-				continue;
+		sibl = cpu + 1;
+
+		for_each_cpu_and_from(sibl, siblmsk, nmsk) {
+			if (cpus_per_grp-- == 0)
+				return;
+
+			cpumask_clear_cpu(sibl, nmsk);
 			cpumask_set_cpu(sibl, irqmsk);
-			cpus_per_grp--;
 		}
 	}
 }
-- 
2.40.1