Re: [PATCH v2 7/7] sched/fair: Use full weight to __calc_delta()

[Vincent Guittot]

On Thu, 19 Feb 2026 at 09:10, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> Since we now use the full weight for avg_vruntime(), also make
> __calc_delta() use the full value.
>
> Since weight is effectively NICE_0_LOAD, this is 20 bits on 64bit.
> This leaves 44 bits for delta_exec, which is ~16k seconds, way longer
> than any one tick would ever be, so no worry about overflow.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
> Tested-by: Shubhang Kaushik <shubhang@xxxxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>


> ---
>  kernel/sched/fair.c |    7 +++++++
>  1 file changed, 7 insertions(+)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -225,6 +225,7 @@ void __init sched_init_granularity(void)
>         update_sysctl();
>  }
>
> +#ifndef CONFIG_64BIT
>  #define WMULT_CONST    (~0U)
>  #define WMULT_SHIFT    32
>
> @@ -283,6 +284,12 @@ static u64 __calc_delta(u64 delta_exec,
>
>         return mul_u64_u32_shr(delta_exec, fact, shift);
>  }
> +#else
> +static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
> +{
> +       return (delta_exec * weight) / lw->weight;
> +}
> +#endif
>
>  /*
>   * delta /= w
>
>