* Re: [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu()
2025-09-11 2:34 [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu() Yury Norov
@ 2025-09-11 6:44 ` K Prateek Nayak
2025-09-11 6:45 ` Madadi Vineeth Reddy
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: K Prateek Nayak @ 2025-09-11 6:44 UTC (permalink / raw)
To: Yury Norov, Ingo Molnar, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, linux-kernel
Hello Yury,
On 9/11/2025 8:04 AM, Yury Norov wrote:
> From: Yury Norov (NVIDIA) <yury.norov@gmail.com>
>
> cpumask_empty() call is O(N) and useless, because the previous
> cpumask_and() returns false for empty 'cpus'.
I agree. Please feel free to include:
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
>
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
> ---
> kernel/sched/fair.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b173a059315c..7229339cbb1b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8320,9 +8320,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> int max_spare_cap_cpu = -1;
> int fits, max_fits = -1;
>
> - cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
> -
> - if (cpumask_empty(cpus))
> + if (!cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask))
> continue;
>
> /* Account external pressure for the energy estimation */
--
Thanks and Regards,
Prateek
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu()
2025-09-11 2:34 [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu() Yury Norov
2025-09-11 6:44 ` K Prateek Nayak
@ 2025-09-11 6:45 ` Madadi Vineeth Reddy
2025-09-11 8:28 ` Vincent Guittot
2025-09-11 14:00 ` Markus Elfring
3 siblings, 0 replies; 5+ messages in thread
From: Madadi Vineeth Reddy @ 2025-09-11 6:45 UTC (permalink / raw)
To: Yury Norov
Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
Valentin Schneider, linux-kernel, Madadi Vineeth Reddy
On 11/09/25 08:04, Yury Norov wrote:
> From: Yury Norov (NVIDIA) <yury.norov@gmail.com>
>
> cpumask_empty() call is O(N) and useless, because the previous
> cpumask_and() returns false for empty 'cpus'.
>
LGTM
Reviewed-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Thanks,
Madadi Vineeth Reddy
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
> ---
> kernel/sched/fair.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b173a059315c..7229339cbb1b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8320,9 +8320,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> int max_spare_cap_cpu = -1;
> int fits, max_fits = -1;
>
> - cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
> -
> - if (cpumask_empty(cpus))
> + if (!cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask))
> continue;
>
> /* Account external pressure for the energy estimation */
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu()
2025-09-11 2:34 [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu() Yury Norov
2025-09-11 6:44 ` K Prateek Nayak
2025-09-11 6:45 ` Madadi Vineeth Reddy
@ 2025-09-11 8:28 ` Vincent Guittot
2025-09-11 14:00 ` Markus Elfring
3 siblings, 0 replies; 5+ messages in thread
From: Vincent Guittot @ 2025-09-11 8:28 UTC (permalink / raw)
To: Yury Norov
Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman, Valentin Schneider,
linux-kernel
On Thu, 11 Sept 2025 at 04:34, Yury Norov <yury.norov@gmail.com> wrote:
>
> From: Yury Norov (NVIDIA) <yury.norov@gmail.com>
>
> cpumask_empty() call is O(N) and useless, because the previous
> cpumask_and() returns false for empty 'cpus'.
>
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> kernel/sched/fair.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b173a059315c..7229339cbb1b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8320,9 +8320,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> int max_spare_cap_cpu = -1;
> int fits, max_fits = -1;
>
> - cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
> -
> - if (cpumask_empty(cpus))
> + if (!cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask))
> continue;
>
> /* Account external pressure for the energy estimation */
> --
> 2.43.0
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu()
2025-09-11 2:34 [PATCH] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu() Yury Norov
` (2 preceding siblings ...)
2025-09-11 8:28 ` Vincent Guittot
@ 2025-09-11 14:00 ` Markus Elfring
3 siblings, 0 replies; 5+ messages in thread
From: Markus Elfring @ 2025-09-11 14:00 UTC (permalink / raw)
To: Yury Norov, kernel-janitors, Ben Segall, Dietmar Eggemann,
Ingo Molnar, Juri Lelli, Mel Gorman, Peter Zijlstra,
Steven Rostedt, Valentin Schneider, Vincent Guittot
Cc: LKML, K Prateek Nayak, Madadi Vineeth Reddy
> cpumask_empty() call is O(N) and useless, because the previous
> cpumask_and() returns false for empty 'cpus'.
It seems to be more helpful to reuse a return value from a previous function call.
How do you think about to add any tags (like “Fixes” and “Cc”) accordingly?
See also:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.17-rc5#n94
Regards,
Markus
^ permalink raw reply [flat|nested] 5+ messages in thread