linux-kernel - Re: [RFC PATCH 2/6] sched/dl: Capacity-aware migrations

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Message-ID: <20190508080436.GF6551@localhost.localdomain>
Date:   Wed, 8 May 2019 10:04:36 +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 2/6] sched/dl: Capacity-aware migrations

Hi Luca,

On 06/05/19 06:48, Luca Abeni wrote:
> From: luca abeni <luca.abeni@...tannapisa.it>
> 
> Currently, the SCHED_DEADLINE scheduler uses a global EDF scheduling
> algorithm, migrating tasks to CPU cores without considering the core
> capacity and the task utilization. This works well on homogeneous
> systems (SCHED_DEADLINE tasks are guaranteed to have a bounded
> tardiness), but presents some issues on heterogeneous systems. For
> example, a SCHED_DEADLINE task might be migrated on a core that has not
> enough processing capacity to correctly serve the task (think about a
> task with runtime 70ms and period 100ms migrated to a core with
> processing capacity 0.5)
> 
> This commit is a first step to address the issue: When a task wakes
> up or migrates away from a CPU core, the scheduler tries to find an
> idle core having enough processing capacity to serve the task.
> 
> Signed-off-by: luca abeni <luca.abeni@...tannapisa.it>
> ---
>  kernel/sched/cpudeadline.c | 31 +++++++++++++++++++++++++++++--
>  kernel/sched/deadline.c    |  8 ++++++--
>  kernel/sched/sched.h       |  7 ++++++-
>  3 files changed, 41 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index 50316455ea66..d21f7905b9c1 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -110,6 +110,22 @@ static inline int cpudl_maximum(struct cpudl *cp)
>  	return cp->elements[0].cpu;
>  }
>  
> +static inline int dl_task_fit(const struct sched_dl_entity *dl_se,
> +			      int cpu, u64 *c)
> +{
> +	u64 cap = (arch_scale_cpu_capacity(NULL, cpu) * arch_scale_freq_capacity(cpu)) >> SCHED_CAPACITY_SHIFT;
> +	s64 rel_deadline = dl_se->dl_deadline;
> +	u64 rem_runtime  = dl_se->dl_runtime;

This is not the dynamic remaining one, is it?

I see however 4/6.. lemme better look at that.

Best,

- Juri