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

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Date:	Tue, 8 Sep 2015 17:55:02 +0900
From:	"byungchul.park" <byungchul.park@....com>
To:	"'Wanpeng Li'" <wanpeng.li@...mail.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()



> -----Original Message-----
> From: Wanpeng Li [mailto:wanpeng.li@...mail.com]
> Sent: Tuesday, September 08, 2015 5:46 PM
> To: Byungchul Park
> Cc: Peter Zijlstra; Ingo Molnar; 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.

Ah.. Ok. What you are pointing out against, is this commit.
I will focus on verifying if this commit is wrong or not from now.
Let me think about this commit more.

Thanks,
byungchul

> 
> Regards,
> Wanpeng Li

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