linux-kernel - Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to

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Date:	Tue, 8 Sep 2015 16:38:52 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Byungchul Park <byungchul.park@....com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	yuyang.du@...el.com
Subject: Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair()

On 9/8/15 4:22 PM, Byungchul Park wrote:
> On Tue, Sep 08, 2015 at 04:04:49PM +0800, Wanpeng Li wrote:
>>>> However, if se->vruntime -= cfs_rq->min_vruntime is positive, the
>>>> behavior is different after your patch. e.g. se->vruntime(the
>>>> relative vruntime in switched_to_fair()) < min_vruntime -
>>>> sysctl_sched_latency/2
>>>>
>>>> before your patch:
>>>>
>>>> se->vruntime = min_vruntime - sysctl_sched_latency/2 (place_entity())
>>> my patch is based on ff277d4 commit at tip/sched/core.
>>>
>>> there's no change between before and after.
>>>
>>> check it please.
>>>
>>> and this logic seems to be no problem to me. :(
>> Your logic will lose fair sleeper bonus in the scenario which I pointed out.
> i mean in ff277d4 commit:

Please include the commit subject when you point out a commit, do you 
mean this one?

commit ff277d4250fe715b6666219b1a3423b863418794
Author: Andrea Parri <parri.andrea@...il.com>
Date:   Wed Aug 5 15:56:19 2015 +0200

     sched/deadline: Fix comment in enqueue_task_dl()

     The "dl_boosted" flag is set by comparing *absolute* deadlines
     (c.f., rt_mutex_setprio()).


What's the relationship w/ this patch?

Regards,
Wanpeng Li

>
> se->vruntime += cfs->min_vruntime  (switched_to_fair())
> se->vruntime = se->vruntime or bonused value (place_entity())
>
> after my patch:
>
> se->vruntime += cfs->min_vruntime  (switched_to_fair())
> se->vruntime = se->vruntime or bonused value (place_entity())
>
> ---
>
> SAME!!!
>
> in addtion, se->vruntime already had a bonused value if eligible,
> when it was detached from cfs_rq.
>
>>>> after your patch:
>>>>
>>>> se->vruntime += cfs->min_vruntime  (switched_to_fair())
>>>> se->vruntime = se->vruntime  (place_entity())
>>>>
>>>>
>>>> Regards,
>>>> Wanpeng Li
>>>>
>>>> --
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>> --
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