linux-kernel - Re: [PATCH 1/3] sched/deadline: clear dl_entity params when setscheduling to different class

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Message-ID: <54465C77.8070209@arm.com>
Date:	Tue, 21 Oct 2014 14:15:35 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Wanpeng Li <kernellwp@...il.com>,
	"peterz@...radead.org" <peterz@...radead.org>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"juri.lelli@...il.com" <juri.lelli@...il.com>,
	"raistlin@...ux.it" <raistlin@...ux.it>,
	"michael@...rulasolutions.com" <michael@...rulasolutions.com>,
	"fchecconi@...il.com" <fchecconi@...il.com>,
	"daniel.wagner@...-carit.de" <daniel.wagner@...-carit.de>,
	"vincent@...out.info" <vincent@...out.info>,
	"luca.abeni@...tn.it" <luca.abeni@...tn.it>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] sched/deadline: clear dl_entity params when setscheduling
 to different class

Hi,

On 21/10/14 13:15, Wanpeng Li wrote:
> ping,
> 
> 于 10/8/14, 8:32 PM, Wanpeng Li 写道:
>> Hi Juri,
>>
>> 于 9/19/14, 5:22 PM, Juri Lelli 写道:
>>> When a task is using SCHED_DEADLINE and the user setschedules it to a 
>>> different
>>> class its sched_dl_entity static parameters are not cleaned up. This 
>>> causes a
>>> bug if the user sets it back to SCHED_DEADLINE with the same 
>>> parameters again.
>>> The problem resides in the check we perform at the very beginning of
>>> dl_overflow():
>>>
>>>     if (new_bw == p->dl.dl_bw)
>>>         return 0;
>>>
>>> This condition is met in the case depicted above, so the function 
>>> returns and
>>> dl_b->total_bw is not updated (the p->dl.dl_bw is not added to it). 
>>> After this,
>>
>> As you know there is no static parameter clear before this patch, so 
>> if p->dl.dl_bw will decrease from dl_b->total_bw when the user 
>> setschedules to a different class instead of dl?
>>

We remove p->dl.dl_bw from dl_b->total_bw in dl_overflow(). Then this
patch introduces the clearing of p->dl params.

Thanks,

- Juri

>> Regards,
>> Wanpeng Li
>>
>>> admission control is broken.
>>>
>>> This patch fixes the thing, properly clearing static parameters for a 
>>> task
>>> that ceases to use SCHED_DEADLINE.
>>>
>>> Reported-by: Daniele Alessandrelli <daniele.alessandrelli@...il.com>
>>> Reported-by: Daniel Wagner <daniel.wagner@...-carit.de>
>>> Reported-by: Vincent Legout <vincent@...out.info>
>>> Tested-by: Luca Abeni <luca.abeni@...tn.it>
>>> Signed-off-by: Juri Lelli <juri.lelli@....com>
>>> Cc: Ingo Molnar <mingo@...hat.com>
>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>> Cc: Juri Lelli <juri.lelli@...il.com>
>>> Cc: Dario Faggioli <raistlin@...ux.it>
>>> Cc: Michael Trimarchi <michael@...rulasolutions.com>
>>> Cc: Fabio Checconi <fchecconi@...il.com>
>>> Cc: linux-kernel@...r.kernel.org
>>> ---
>>>   kernel/sched/core.c     | 19 +++++++++++++++----
>>>   kernel/sched/deadline.c |  2 ++
>>>   kernel/sched/sched.h    |  3 +++
>>>   3 files changed, 20 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index ec1a286..581a429 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -1776,6 +1776,20 @@ int wake_up_state(struct task_struct *p, 
>>> unsigned int state)
>>>   }
>>>     /*
>>> + * This function clears the sched_dl_entity static params.
>>> + */
>>> +void __dl_clear_params(struct task_struct *p)
>>> +{
>>> +    struct sched_dl_entity *dl_se = &p->dl;
>>> +
>>> +    dl_se->dl_runtime = 0;
>>> +    dl_se->dl_deadline = 0;
>>> +    dl_se->dl_period = 0;
>>> +    dl_se->flags = 0;
>>> +    dl_se->dl_bw = 0;
>>> +}
>>> +
>>> +/*
>>>    * Perform scheduler related setup for a newly forked process p.
>>>    * p is forked by current.
>>>    *
>>> @@ -1799,10 +1813,7 @@ static void __sched_fork(unsigned long 
>>> clone_flags, struct task_struct *p)
>>>         RB_CLEAR_NODE(&p->dl.rb_node);
>>>       hrtimer_init(&p->dl.dl_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>>> -    p->dl.dl_runtime = p->dl.runtime = 0;
>>> -    p->dl.dl_deadline = p->dl.deadline = 0;
>>> -    p->dl.dl_period = 0;
>>> -    p->dl.flags = 0;
>>> +    __dl_clear_params(p);
>>>         INIT_LIST_HEAD(&p->rt.run_list);
>>>   diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>>> index 255ce13..4a51b14 100644
>>> --- a/kernel/sched/deadline.c
>>> +++ b/kernel/sched/deadline.c
>>> @@ -1569,6 +1569,8 @@ static void switched_from_dl(struct rq *rq, 
>>> struct task_struct *p)
>>>       if (hrtimer_active(&p->dl.dl_timer) && !dl_policy(p->policy))
>>>           hrtimer_try_to_cancel(&p->dl.dl_timer);
>>>   +    __dl_clear_params(p);
>>> +
>>>   #ifdef CONFIG_SMP
>>>       /*
>>>        * Since this might be the only -deadline task on the rq,
>>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>>> index 579712f..4890484 100644
>>> --- a/kernel/sched/sched.h
>>> +++ b/kernel/sched/sched.h
>>> @@ -126,6 +126,9 @@ struct rt_bandwidth {
>>>       u64            rt_runtime;
>>>       struct hrtimer        rt_period_timer;
>>>   };
>>> +
>>> +void __dl_clear_params(struct task_struct *p);
>>> +
>>>   /*
>>>    * To keep the bandwidth of -deadline tasks and groups under control
>>>    * we need some place where:
>>
> 
> 

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