linux-kernel - [PATCH v2 3/6] lib/group_cpus: optimize inner loop in grp_spread_init

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Message-Id: <20231207203900.859776-4-yury.norov@gmail.com>
Date:   Thu,  7 Dec 2023 12:38:57 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>, Ming Lei <ming.lei@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH v2 3/6] 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 8eb18c6bbf3b..7ac94664230f 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;
 		}
 	}
 }
-- 
2.40.1