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Message-Id: <20231207134521.c921cb0bb1ab7487d78aeb07@linux-foundation.org>
Date: Thu, 7 Dec 2023 13:45:21 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Yury Norov <yury.norov@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
Ming Lei <ming.lei@...hat.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v2 3/6] lib/group_cpus: optimize inner loop in
grp_spread_init_one()
On Thu, 7 Dec 2023 12:38:57 -0800 Yury Norov <yury.norov@...il.com> wrote:
> 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.
>
> --- 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;
I assume this test goes away because the iterator takes care of it?
> + 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;
> }
> }
> }
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