linux-kernel - Re: [PATCH] sched/fair: Do not decay new task load on first enqueue

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Date:   Wed, 9 Nov 2016 17:53:56 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Matt Fleming <matt@...eblueprint.co.uk>,
        Wanpeng Li <kernellwp@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Yuyang Du <yuyang.du@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH] sched/fair: Do not decay new task load on first enqueue

On 19 October 2016 at 11:53, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Oct 19, 2016 at 08:38:12AM +0200, Vincent Guittot wrote:
>> > It might make sense to have helper functions to evaluate those
>>
>> The main issue is the number of parameters used in these conditions
>> that makes helper function not really more readable.
>
> Fair enough I suppose..
>
>> > conditions, because currently there's two instances of each, once in the
>> > branch selection and then again (but inverted, we miss the == case fwiw)
>>
>> not sure to catch the comment about inverted and miss the == case
>
> Oh, you're right. Which proves my point on this not being entirely
> readable :/

Hi Peter,

I'm not sure of the status of this patch.
It seems difficult to get a more readable code.
Do you want me to add more comments about when we enter each state or
current version is enough ?

Vincent

>
> Initially I thought the things were of the form:
>
>         else if (ineq) {
>         }
>
>         ...
>
>         if (... || !ineq || ...)
>
>
> Which would get you things like: a<b, !a<b := a>b, and leave a==b
> undefined. But if I put them along side one another like:
>
>
> +               } else if (min_runnable_load > (runnable_load + imbalance)) {
>
> +                         (min_runnable_load > (this_runnable_load + imbalance)) ||
>
>
> +               } else if ((runnable_load < (min_runnable_load + imbalance)) &&
> +                               (100*min_avg_load > sd->imbalance_pct*avg_load)) {
>
> +                    ((this_runnable_load < (min_runnable_load + imbalance)) &&
> +                               (100*min_avg_load > sd->imbalance_pct*this_avg_load)))
>
> We can see this is not in fact the case.
>
> Blergh, I also cannot see a pretty way to increase readability here,
> because while they have the same general shape, there's this small
> variation with this_*.
>
> A well..