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Date:   Mon, 29 Jul 2019 10:57:11 +0200
From:   Juri Lelli <juri.lelli@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@kernel.org, linux-kernel@vger.kernel.org,
        dietmar.eggemann@arm.com, luca.abeni@santannapisa.it,
        bristot@redhat.com, balsini@android.com, dvyukov@google.com,
        tglx@linutronix.de, vpillai@digitalocean.com, rostedt@goodmis.org
Subject: Re: [RFC][PATCH 01/13] sched/deadline: Impose global limits on
 sched_attr::sched_period
Message-ID: <20190729085711.GQ25636@localhost.localdomain>
References: <20190726145409.947503076@infradead.org>
 <20190726161357.397880775@infradead.org>
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Hi,

On 26/07/19 16:54, Peter Zijlstra wrote:
> 
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Luca Abeni <luca.abeni@santannapisa.it>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/linux/sched/sysctl.h |    3 +++
>  kernel/sched/deadline.c      |   23 +++++++++++++++++++++--
>  kernel/sysctl.c              |   14 ++++++++++++++
>  3 files changed, 38 insertions(+), 2 deletions(-)
> 
> --- a/include/linux/sched/sysctl.h
> +++ b/include/linux/sched/sysctl.h
> @@ -56,6 +56,9 @@ int sched_proc_update_handler(struct ctl
>  extern unsigned int sysctl_sched_rt_period;
>  extern int sysctl_sched_rt_runtime;
>  
> +extern unsigned int sysctl_sched_dl_period_max;
> +extern unsigned int sysctl_sched_dl_period_min;
> +
>  #ifdef CONFIG_UCLAMP_TASK
>  extern unsigned int sysctl_sched_uclamp_util_min;
>  extern unsigned int sysctl_sched_uclamp_util_max;
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2597,6 +2597,14 @@ void __getparam_dl(struct task_struct *p
>  }
>  
>  /*
> + * Default limits for DL period; on the top end we guard against small util
> + * tasks still getting rediculous long effective runtimes, on the bottom end we

s/rediculous/ridiculous/

> + * guard against timer DoS.
> + */
> +unsigned int sysctl_sched_dl_period_max = 1 << 22; /* ~4 seconds */
> +unsigned int sysctl_sched_dl_period_min = 100;     /* 100 us */

These limits look sane to me. I've actually been experimenting with 10us
period tasks and throttling seemed to behave fine, but I guess 100us is
a saner default.

So, (with a few lines of changelog :)

Acked-by: Juri Lelli <juri.lelli@redhat.com>

Thanks for doing this.

Best,

Juri