linux-kernel - Re: [PATCHv4 00/12] sched/fair: Migrate 'misfit' tasks on asymmetric capacity systems

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Date:   Thu, 16 Aug 2018 18:57:41 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Morten Rasmussen <morten.rasmussen@....com>
Cc:     peterz@...radead.org, mingo@...hat.com, valentin.schneider@....com,
        dietmar.eggemann@....com, vincent.guittot@...aro.org,
        gaku.inami.xh@...esas.com, linux-kernel@...r.kernel.org,
        tkjos@...gle.com
Subject: Re: [PATCHv4 00/12] sched/fair: Migrate 'misfit' tasks on asymmetric
 capacity systems

On Wed, Jul 04, 2018 at 11:17:38AM +0100, Morten Rasmussen wrote:
> On asymmetric cpu capacity systems (e.g. Arm big.LITTLE) it is crucial
> for performance that cpu intensive tasks are aggressively migrated to
> high capacity cpus as soon as those become available. The capacity
> awareness tweaks already in the wake-up path can't handle this as such
> tasks might run or be runnable forever. If they happen to be placed on a
> low capacity cpu from the beginning they are stuck there forever while
> high capacity cpus may have become available in the meantime.
> 
> To address this issue this patch set introduces a new "misfit"
> load-balancing scenario in periodic/nohz/newly idle balance which tweaks
> the load-balance conditions to ignore load per capacity in certain
> cases. Since misfit tasks are commonly running alone on a cpu, more
> aggressive active load-balancing is needed too.
> 
> The fundamental idea of this patch set has been in Android kernels for a
> long time and is absolutely essential for consistent performance on
> asymmetric cpu capacity systems.
> 
> The patches have been tested on:
>    1. Arm Juno (r0): 2+4 Cortex A57/A53
>    2. Hikey960: 4+4 Cortex A73/A53
> 

Thanks for posting these, we have been carrying it in the Android Common
Kernel for some time. They have been useful for Android systems.

Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

thanks,

 - Joel