Re: [RFC PATCH 03/16] sched/pelt: Add a new function to approximate runtime to reach given util
From: Sultan Alsawaf (unemployed)
Date: Thu Aug 22 2024 - 01:37:09 EST
On Tue, Aug 20, 2024 at 05:34:59PM +0100, Qais Yousef wrote:
> It is basically the ramp-up time from 0 to a given value. Will be used
> later to implement new tunable to control response time for schedutil.
>
> Signed-off-by: Qais Yousef <qyousef@xxxxxxxxxxx>
> ---
> kernel/sched/pelt.c | 21 +++++++++++++++++++++
> kernel/sched/sched.h | 1 +
> 2 files changed, 22 insertions(+)
>
> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> index 2ce83e880bd5..06cb881ba582 100644
> --- a/kernel/sched/pelt.c
> +++ b/kernel/sched/pelt.c
> @@ -487,3 +487,24 @@ unsigned long approximate_util_avg(unsigned long util, u64 delta)
>
> return sa.util_avg;
> }
> +
> +/*
> + * Approximate the required amount of runtime in ms required to reach @util.
> + */
> +u64 approximate_runtime(unsigned long util)
> +{
> + struct sched_avg sa = {};
> + u64 delta = 1024; // period = 1024 = ~1ms
> + u64 runtime = 0;
> +
> + if (unlikely(!util))
> + return runtime;
Seems like this check can be removed since it's covered by the loop condition.
> +
> + while (sa.util_avg < util) {
> + accumulate_sum(delta, &sa, 1, 0, 1);
> + ___update_load_avg(&sa, 0);
> + runtime++;
> + }
I think this could be a lookup table (probably 1024 * u8), for constant-time
runtime approximation.
> +
> + return runtime;
> +}
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 294c6769e330..47f158b2cdc2 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -3065,6 +3065,7 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> unsigned long max);
>
> unsigned long approximate_util_avg(unsigned long util, u64 delta);
> +u64 approximate_runtime(unsigned long util);
>
> /*
> * Verify the fitness of task @p to run on @cpu taking into account the
> --
> 2.34.1
>
Cheers,
Sultan