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

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Message-ID: <YD0ik65KwwU5R4Rv@hirez.programming.kicks-ass.net>
Date:   Mon, 1 Mar 2021 18:21:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Vincent Donnefort <vincent.donnefort@....com>, mingo@...dhat.com,
        vincent.guittot@...aro.org, 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 Mon, Mar 01, 2021 at 05:34:09PM +0100, Dietmar Eggemann wrote:
> On 26/02/2021 09:41, Peter Zijlstra wrote:
> > 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.
> 
> I guess because it was only ever used in util_est for last_ewma_diff.
> 
> It's now used for last_ewma_diff and last_enqueued_diff, still only for
> util_est though and both times with the same margin
> (SCHED_CAPACITY_SCALE / 100)).
> 
> Vincent D. should be back on Wed from hols.

Fair enough; I've un-done it but kept the rest of the patch.