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

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Message-ID: <54464E79.2050601@gmail.com>
Date:	Tue, 21 Oct 2014 20:15:53 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Juri Lelli <juri.lelli@....com>, peterz@...radead.org
CC:	mingo@...hat.com, juri.lelli@...il.com, raistlin@...ux.it,
	michael@...rulasolutions.com, fchecconi@...il.com,
	daniel.wagner@...-carit.de, vincent@...out.info,
	luca.abeni@...tn.it, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] sched/deadline: clear dl_entity params when setscheduling
 to different class

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?
>
> 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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