linux-kernel - Re: [PATCH v2] sched/pelt: Fix task util

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Date:   Fri, 26 Feb 2021 09:41:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Donnefort <vincent.donnefort@....com>
Cc:     mingo@...dhat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, linux-kernel@...r.kernel.org,
        patrick.bellasi@...bug.net, valentin.schneider@....com
Subject: Re: [PATCH v2] sched/pelt: Fix task util_est update filtering

On Thu, Feb 25, 2021 at 04:58:20PM +0000, Vincent Donnefort wrote:
> +#define UTIL_EST_MARGIN (SCHED_CAPACITY_SCALE / 100)
> +
>  /*
> - * Check if a (signed) value is within a specified (unsigned) margin,
> + * Check if a (signed) value is within the (unsigned) util_est margin,
>   * based on the observation that:
>   *
>   *     abs(x) < y := (unsigned)(x + y - 1) < (2 * y - 1)
>   *
> - * NOTE: this only works when value + maring < INT_MAX.
> + * NOTE: this only works when value + UTIL_EST_MARGIN < INT_MAX.
>   */
> -static inline bool within_margin(int value, int margin)
> +static inline bool util_est_within_margin(int value)
>  {
> -	return ((unsigned int)(value + margin - 1) < (2 * margin - 1));
> +	return ((unsigned int)(value + UTIL_EST_MARGIN - 1) <
> +		(2 * UTIL_EST_MARGIN - 1));
>  }

> -	if (within_margin(last_ewma_diff, (SCHED_CAPACITY_SCALE / 100)))
> +	if (util_est_within_margin(last_ewma_diff)) {

What was the purpose of this change? What was a generic helper is now
super specific.