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Date:   Thu, 21 May 2020 15:45:58 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        dietmar.eggemann@....com, luca.abeni@...tannapisa.it,
        balsini@...roid.com, dvyukov@...gle.com, tglx@...utronix.de,
        vpillai@...italocean.com, rostedt@...dmis.org
Subject: Re: [RFC][PATCH 01/13] sched/deadline: Impose global limits on
 sched_attr::sched_period

On 5/20/20 8:38 PM, Juri Lelli wrote:
> Hi Peter,
> 
> On 26/07/19 16:54, Peter Zijlstra wrote:
>> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
>> Cc: Luca Abeni <luca.abeni@...tannapisa.it>
>> Cc: Juri Lelli <juri.lelli@...hat.com>
>> Cc: Dmitry Vyukov <dvyukov@...gle.com>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.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),
> I think this never made it upstream. And I believe both me and Daniel
> were OK with it. Do you recall if any additional change was needed?

Just to confirm, yes I am OK with it!

-- Daniel

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