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Subject: Re: [PATCH v2] sched/pelt: Fix task util_est update filtering
To:     Peter Zijlstra <peterz@infradead.org>,
        Vincent Donnefort <vincent.donnefort@arm.com>
Cc:     mingo@readhat.com, vincent.guittot@linaro.org,
        linux-kernel@vger.kernel.org, patrick.bellasi@matbug.net,
        valentin.schneider@arm.com
References: <20210225165820.1377125-1-vincent.donnefort@arm.com>
 <YDi0Ip11fpOubQqz@hirez.programming.kicks-ass.net>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <b1471e3a-e8c5-3ab4-5db4-0084612ade55@arm.com>
Date:   Mon, 1 Mar 2021 17:34:09 +0100
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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.