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From: Alessio Balsini <balsini@android.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, juri.lelli@redhat.com,
	linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com,
	luca.abeni@santannapisa.it, bristot@redhat.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
Date: Fri, 2 Aug 2019 18:21:04 +0100
Message-ID: <20190802172104.GA134279@google.com> (raw)
In-Reply-To: <20190726161357.397880775@infradead.org>

Hi Peter,

This is indeed an important missing piece.

I think it would be worth having some simple checks, e.g.:
- period_min <= period_max;
- period_min >= (1ULL << DL_SCALE).

To be even more picky, I'm wondering if it would be a good practice to
fail the write operation if there are already dl-tasks in the system
that violate the new constraint.  I'm afraid there is no cheap way of
achieving such check, so, I think we can skip this last tricky thing for
now.

Thanks,
Alessio

On Fri, Jul 26, 2019 at 04:54:10PM +0200, 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
> + * 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 */
> +
> +/*
>   * This function validates the new parameters of a -deadline task.
>   * We ask for the deadline not being zero, and greater or equal
>   * than the runtime, as well as the period of being zero or
> @@ -2608,6 +2616,8 @@ void __getparam_dl(struct task_struct *p
>   */
>  bool __checkparam_dl(const struct sched_attr *attr)
>  {
> +	u64 period, max, min;
> +
>  	/* special dl tasks don't actually use any parameter */
>  	if (attr->sched_flags & SCHED_FLAG_SUGOV)
>  		return true;
> @@ -2631,12 +2641,21 @@ bool __checkparam_dl(const struct sched_
>  	    attr->sched_period & (1ULL << 63))
>  		return false;
>  
> +	period = attr->sched_period;
> +	if (!period)
> +		period = attr->sched_deadline;
> +
>  	/* runtime <= deadline <= period (if period != 0) */
> -	if ((attr->sched_period != 0 &&
> -	     attr->sched_period < attr->sched_deadline) ||
> +	if (period < attr->sched_deadline ||
>  	    attr->sched_deadline < attr->sched_runtime)
>  		return false;
>  
> +	max = (u64)READ_ONCE(sysctl_sched_dl_period_max) * NSEC_PER_USEC;
> +	min = (u64)READ_ONCE(sysctl_sched_dl_period_min) * NSEC_PER_USEC;
> +
> +	if (period < min || period > max)
> +		return false;
> +
>  	return true;
>  }
>  
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -443,6 +443,20 @@ static struct ctl_table kern_table[] = {
>  		.proc_handler	= sched_rt_handler,
>  	},
>  	{
> +		.procname	= "sched_deadline_period_max_us",
> +		.data		= &sysctl_sched_dl_period_max,
> +		.maxlen		= sizeof(unsigned int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec,
> +	},
> +	{
> +		.procname	= "sched_deadline_period_min_us",
> +		.data		= &sysctl_sched_dl_period_min,
> +		.maxlen		= sizeof(unsigned int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec,
> +	},
> +	{
>  		.procname	= "sched_rr_timeslice_ms",
>  		.data		= &sysctl_sched_rr_timeslice,
>  		.maxlen		= sizeof(int),
> 
> 

  parent reply index

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-26 14:54 [RFC][PATCH 00/13] SCHED_DEADLINE server infrastructure Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 01/13] sched/deadline: Impose global limits on sched_attr::sched_period Peter Zijlstra
2019-07-29  8:57   ` Juri Lelli
2019-07-29 11:45     ` Daniel Bristot de Oliveira
2019-08-02 17:21   ` Alessio Balsini [this message]
2019-08-05 11:53     ` Peter Zijlstra
2019-08-22 12:29       ` Alessio Balsini
2019-08-22 16:51         ` Peter Zijlstra
2019-08-31 14:41           ` Alessio Balsini
2019-09-02  9:16             ` Peter Zijlstra
2019-09-02 12:31               ` Peter Zijlstra
2019-09-04 10:16               ` Steven Rostedt
2019-09-04 11:30                 ` Peter Zijlstra
2019-09-04 13:24                   ` Joel Fernandes
2019-09-04 14:11                     ` Will Deacon
2019-09-04 14:35                       ` Joel Fernandes
2019-09-04 15:52                     ` Peter Zijlstra
2019-10-23 17:17       ` [PATCH 4.4 4.9 4.14] loop: Add LOOP_SET_DIRECT_IO to compat ioctl Alessio Balsini
2019-10-23 17:22         ` Alessio Balsini
2019-10-25  0:17         ` Sasha Levin
2020-05-20 18:38   ` [RFC][PATCH 01/13] sched/deadline: Impose global limits on sched_attr::sched_period Juri Lelli
2020-05-21 13:45     ` Daniel Bristot de Oliveira
2020-06-16 12:21   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 02/13] stop_machine: Fix stop_cpus_in_progress ordering Peter Zijlstra
2019-07-30 13:16   ` Phil Auld
2019-07-30 13:22   ` Steven Rostedt
2019-07-26 14:54 ` [RFC][PATCH 03/13] sched: Fix kerneldoc comment for ia64_set_curr_task Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Peter Zijlstra
2019-07-29  9:25   ` Juri Lelli
2019-07-29 11:15     ` Peter Zijlstra
2019-07-29 11:27       ` Juri Lelli
2019-07-29 13:04         ` Peter Zijlstra
2019-07-29 13:17           ` Juri Lelli
2019-07-29 14:40             ` Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 05/13] sched: Add task_struct pointer to sched_class::set_curr_task Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 06/13] sched/fair: Export newidle_balance() Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 07/13] sched: Allow put_prev_task() to drop rq->lock Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 08/13] sched: Rework pick_next_task() slow-path Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 09/13] sched: Unify runtime accounting across classes Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 10/13] sched/deadline: Collect sched_dl_entity initialization Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 11/13] sched/deadline: Move bandwidth accounting into {en,de}queue_dl_entity Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 12/13] sched/deadline: Introduce deadline servers Peter Zijlstra
2019-08-07 16:31   ` Dietmar Eggemann
2019-08-08  6:52     ` Juri Lelli
2019-08-08  7:52       ` Dietmar Eggemann
2019-08-08  7:56     ` Peter Zijlstra
2019-08-08  8:11       ` Dietmar Eggemann
2019-08-08  8:46         ` Juri Lelli
2019-08-08  8:57           ` Dietmar Eggemann
2019-08-08  9:27             ` Juri Lelli
2019-08-08  9:45               ` Juri Lelli
2019-08-30 11:24                 ` Peter Zijlstra
2019-09-06  9:36                   ` Juri Lelli
2019-08-08 10:31           ` Peter Zijlstra
2019-08-09  7:13             ` Juri Lelli
2019-08-08  6:59   ` Juri Lelli
2019-08-09  9:17   ` Dietmar Eggemann
2019-08-09 12:16     ` Juri Lelli
2019-07-26 14:54 ` [RFC][PATCH 13/13] sched/fair: Add trivial fair server Peter Zijlstra
2019-07-26 20:01 ` [RFC][PATCH 00/13] SCHED_DEADLINE server infrastructure luca abeni
2019-09-03 14:27 ` Alessio Balsini
2019-09-04 10:50   ` Juri Lelli
2019-09-04 11:32     ` Peter Zijlstra

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