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

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Message-ID: <BLU436-SMTP154971898FD3346572DB64480530@phx.gbl>
Date:	Tue, 8 Sep 2015 16:45:46 +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 4:38 PM, Wanpeng Li wrote:
> 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?

I think you mean your commit:

commit 7855a35ac07a350e2cd26f09568a6d8e372be358
Author: Byungchul Park <byungchul.park@....com>
Date:   Mon Aug 10 18:02:55 2015 +0900

     sched: Ensure a task has a non-normalized vruntime when returning 
back to CFS


However, that is wrong in the scenario which I mentioned.

Regards,
Wanpeng Li
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