linux-kernel - Re: [PATCH 2/6] sched/dl: fix yield task artificial overrun

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Message-ID: <54520D13.7020904@arm.com>
Date:	Thu, 30 Oct 2014 10:04:03 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Wanpeng Li <kernellwp@...il.com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"juri.lelli@...il.com" <juri.lelli@...il.com>
Subject: Re: [PATCH 2/6] sched/dl: fix yield task artificial overrun

Hi,

On 29/10/14 22:49, Wanpeng Li wrote:
> Hi Juri,
> 2014/10/30 0:33, Juri Lelli:
>> Hi,
>>
>> On 27/10/14 01:41, Wanpeng Li wrote:
>>> The yield semantic of deadline class is to reduce remaining runtime to
>>> zero, and then update_curr_dl() will stop it. However, comsumed bandwidth
>>> is reduced from the budget of yield task again even if it has already been
>>> set to zero which leads to artificial overrun. This patch fix it by reduce
>>> remaining runtime to zero if there is still remaining runtime after comsumed
>>> bandwidth is accumulated.
>>>
>> Oh, right. But, how about what below instead (with a proper comment
>> and changelog)?
>>
>> Thanks,
>>
>> - Juri
>>
>>  From 108ecdff52b154ea2c79d4aac552ddf1ead871c7 Mon Sep 17 00:00:00 2001
>> From: Juri Lelli <juri.lelli@....com>
>> Date: Wed, 29 Oct 2014 16:09:06 +0000
>> Subject: [PATCH] sched/deadline: fix artificial overrun introduced by
>>   yield_task_dl
>>
>> Signed-off-by: Juri Lelli <juri.lelli@....com>
>> ---
>>   kernel/sched/deadline.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index 2e31a30..db6ad38 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -633,7 +633,7 @@ static void update_curr_dl(struct rq *rq)
>>   
>>   	sched_rt_avg_update(rq, delta_exec);
>>   
>> -	dl_se->runtime -= delta_exec;
>> +	dl_se->runtime -= dl_se->dl_yielded ? 0 : delta_exec;
> 
> +	if (dl_se->dl_yielded && dl_se->runtime > 0)
> +		dl_se->runtime = 0;
> 

We already did this in yield_task_dl(). In update_curr_dl() we now
just have to make sure we don't steal some more runtime from the
task that yielded (but we do all other accounting).

Thanks,

- Juri

> Maybe this can be moved to update_curr_dl().
> 
> I think the consumed bandwidth still should be reduced from remaining 
> runtime even if yield, then the remaining runtime will be reset to 0 if 
> there is still remaining runtime as what my patch do. What's your option?
> 
> Regards,
> Wanpeng Li
> 
>>   	if (dl_runtime_exceeded(rq, dl_se)) {
>>   		__dequeue_task_dl(rq, curr, 0);
>>   		if (likely(start_dl_timer(dl_se, curr->dl.dl_boosted)))
> 
> 

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