Re: [PATCH 1/9] sched: Simplify get_nohz_timer_target()

[Joel Fernandes]

On Sun, Aug 6, 2023 at 9:52 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> Use guards to reduce gotos and simplify control flow.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  kernel/sched/core.c |   15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1097,25 +1097,22 @@ int get_nohz_timer_target(void)
>
>         hk_mask = housekeeping_cpumask(HK_TYPE_TIMER);
>
> -       rcu_read_lock();
> +       guard(rcu)();
> +
>         for_each_domain(cpu, sd) {
>                 for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
>                         if (cpu == i)
>                                 continue;
>
> -                       if (!idle_cpu(i)) {
> -                               cpu = i;
> -                               goto unlock;
> -                       }
> +                       if (!idle_cpu(i))
> +                               return i;
>                 }
>         }
>
>         if (default_cpu == -1)
>                 default_cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
> -       cpu = default_cpu;
> -unlock:
> -       rcu_read_unlock();
> -       return cpu;
> +
> +       return default_cpu;
>  }

Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>

I haven't looked into the actual implementation of the guard stuff,
but rcu_read_lock_guarded() is less of an eyesore to me than
guard(rcu)(); TBH.

thanks,

 - Joel