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

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Date:   Wed, 19 Oct 2016 08:38:12 +0200
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 18 October 2016 at 14:15, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Oct 18, 2016 at 12:29:57PM +0100, Matt Fleming wrote:
>> On Tue, 18 Oct, at 01:10:17PM, Peter Zijlstra wrote:
>> >
>> > I'm entirely lost as to which patch we're talking about by now ;-)
>>
>> Heh, this one from Vincent,
>>
>>   https://lkml.kernel.org/r/20161010173440.GA28945@linaro.org
>
> Ah, right.
>
> Seems like a sensible thing to do, and I suppose I should go finish my
> (and yours) update_rq_clock() patches that supersede the patch referred
> to in that thing and is depended upon.
>
>
> 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.

> 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
The test splits runnable_load_avg is 3 ranges:
[0 .. (min_runnable_load - imbalance)] : use the
runnable_loab_avg/this_runnable_load which is significantly smaller
] (min_runnable_load - imbalance) .. (min_runnable_load + imbalance) [
: min_runnable_load and runnable_loab_avg/this_runnable_load are close
so we compare min_load_avg with avg_load/this_avg_load to choose
[(min_runnable_load + imbalance) .. ULONG_MAX] : use min_runnable_load

The condition is used when we look for the best other group in the
sched_domain and  to compare the local group with this best other
group

> in the return NULL case.
>
>
>