linux-kernel - Re: [PATCH v4 00/10] steal tasks to improve CPU utilization

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Message-ID: <a005fd39-a8f5-439a-0e16-3227000b8a02@arm.com>
Date:   Fri, 1 Feb 2019 15:07:53 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Steve Sistare <steven.sistare@...cle.com>, mingo@...hat.com,
        peterz@...radead.org
Cc:     subhra.mazumdar@...cle.com, dhaval.giani@...cle.com,
        daniel.m.jordan@...cle.com, pavel.tatashin@...rosoft.com,
        matt@...eblueprint.co.uk, umgwanakikbuti@...il.com,
        riel@...hat.com, jbacik@...com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, quentin.perret@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 00/10] steal tasks to improve CPU utilization

On 07/12/2018 20:30, Valentin Schneider wrote:
[...]
> ----->8-----
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 17ab4db..8b5172f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7152,7 +7152,8 @@ done: __maybe_unused;
>         rq_idle_stamp_update(rq);
>  
>         new_tasks = idle_balance(rq, rf);
> -       if (new_tasks == 0)
> +       if (new_tasks == 0 &&
> +           (!static_key_unlikely(&sched_energy_present) || READ_ONCE(rq->rd->overutilized))
>                 new_tasks = try_steal(rq, rf);
>  
>         if (new_tasks)
> -----8<-----
> 

As a heads-up, that should now use sched_energy_enabled() [1], so that'd be:

-----8<-----
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f28df187db24..2eddb40fd368 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7134,7 +7134,8 @@ done: __maybe_unused;
        rq_idle_stamp_update(rq);
 
        new_tasks = idle_balance(rq, rf);
-       if (new_tasks == 0)
+       if (new_tasks == 0 &&
+           (!sched_energy_enabled() || READ_ONCE(rq->rd->overutilized)))
                new_tasks = try_steal(rq, rf);
 
        if (new_tasks)
----->8-----

[1]: f8a696f25ba0 ("sched/core: Give DCE a fighting chance")

[...]