linux-kernel - Re: [PATCH] sched/pelt: Fix bracket typo

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Date:   Wed, 8 Jun 2022 22:14:06 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     龍帆軒 <1030steven@...il.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/pelt: Fix bracket typo

On Wed, 8 Jun 2022 at 18:30, 龍帆軒 <1030steven@...il.com> wrote:
>
>
> Randy Dunlap <rdunlap@...radead.org> 於 2022年6月8日 下午11:33 寫道：
>
>
>
> On 6/8/22 08:00, Steven Lung wrote:
>
> The second bracket describing the range is inverted, this patch
> will fix it.
>
> Signed-off-by: Steven Lung <1030steven@...il.com>
> ---
> kernel/sched/pelt.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> index 0f3107682..ed82cfba9 100644
> --- a/kernel/sched/pelt.c
> +++ b/kernel/sched/pelt.c
> @@ -233,7 +233,7 @@ ___update_load_sum(u64 now, struct sched_avg *sa,
>  * When syncing *_avg with *_sum, we must take into account the current
>  * position in the PELT segment otherwise the remaining part of the segment
>  * will be considered as idle time whereas it's not yet elapsed and this will
> - * generate unwanted oscillation in the range [1002..1024[.
>
>
> Is the above the same as                   range [1002..1024).
> ?  I.e. 1002-1023 inclusive (or 1024 excluded)?

yes, 1024 was excluded from the range because we reached 1024 when
period_contrib == 1024 but when period_contrib == 1024 we decayed and
period_contrib becomes 0 and the load_avg went down to 1002.

Before the changes, the load_avg  for default weight was
1024*(LOAD_AVG_MAX-1024+period_contrib)/LOAD_AVG_MAX
if period_contrib == 0 ie the beg of the window we've got a load_avg of 1002
if period_contrib == 1023 ie the end of the window we've got a load of
int(1023.97)==1023

In French, we use [1002..1024[ but english version is [1002..1024)

>
> + * generate unwanted oscillation in the range [1002..1024].
>  *
>  * The max value of *_sum varies with the position in the time segment and is
>  * equals to :
>
>
> --
> ~Randy
>
>
> In the patch that the author submitted[1] for this comment, he mentioned that the value 1024 can be obtained.
> So I think we should use brackets instead of parenthesis.
>
> [1]: https://lore.kernel.org/all/20200506155301.14288-1-vincent.guittot@linaro.org/T/#u
>
> --
> Steven
>