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SubjectRe: [PATCH v2 2/6] lib/group_cpus: relax atomicity requirement in grp_spread_init_one()
On Thu, Dec 07, 2023 at 12:38:56PM -0800, Yury Norov wrote:
> Because nmsk and irqmsk are stable, extra atomicity is not required.
>
> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> ---
> lib/group_cpus.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/lib/group_cpus.c b/lib/group_cpus.c
> index ee272c4cefcc..8eb18c6bbf3b 100644
> --- a/lib/group_cpus.c
> +++ b/lib/group_cpus.c
> @@ -24,8 +24,8 @@ static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
> if (cpu >= nr_cpu_ids)
> return;
>
> - cpumask_clear_cpu(cpu, nmsk);
> - cpumask_set_cpu(cpu, irqmsk);
> + __cpumask_clear_cpu(cpu, nmsk);
> + __cpumask_set_cpu(cpu, irqmsk);
> cpus_per_grp--;
>
> /* If the cpu has siblings, use them first */
> @@ -34,9 +34,8 @@ static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
> sibl = cpumask_next(sibl, siblmsk);
> if (sibl >= nr_cpu_ids)
> break;
> - if (!cpumask_test_and_clear_cpu(sibl, nmsk))
> - continue;
> - cpumask_set_cpu(sibl, irqmsk);
> + __cpumask_clear_cpu(sibl, nmsk);
> + __cpumask_set_cpu(sibl, irqmsk);
> cpus_per_grp--;

Here the change isn't simply to remove atomicity, and the test
part of cpumask_test_and_clear_cpu() is removed, so logic is changed,
I feel the correct change should be:

if (cpumask_test_cpu(sibl, nmsk)) {
__cpumask_clear_cpu(sibl, nmsk);
__cpumask_set_cpu(sibl, irqmsk);
cpus_per_grp--;
}



Thanks,
Ming

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