linux-kernel - Re: [RFC PATCH 3/6] sched/dl: Try better placement even for deadline tasks that do not block

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Message-ID: <20190508080116.GE6551@localhost.localdomain>
Date:   Wed, 8 May 2019 10:01:16 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Luca Abeni <luca.abeni@...tannapisa.it>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Quentin Perret <quentin.perret@....com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
Subject: Re: [RFC PATCH 3/6] sched/dl: Try better placement even for deadline
 tasks that do not block

Hi Luca,

On 06/05/19 06:48, Luca Abeni wrote:
> From: luca abeni <luca.abeni@...tannapisa.it>
> 
> Currently, the scheduler tries to find a proper placement for
> SCHED_DEADLINE tasks when they are pushed out of a core or when
> they wake up. Hence, if there is a single SCHED_DEADLINE task
> that never blocks and wakes up, such a task is never migrated to
> an appropriate CPU core, but continues to execute on its original
> core.
> 
> This commit addresses the issue by trying to migrate a SCHED_DEADLINE
> task (searching for an appropriate CPU core) the first time it is
> throttled.

Why we failed to put the task on a CPU with enough (max) capacity right
after it passed admission control? The very first time the task was
scheduled I mean.

Thanks,

- Juri