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

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Message-ID: <20150908082239.GK6455@byungchulpark-X58A-UD3R>
Date:	Tue, 8 Sep 2015 17:22:40 +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()

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:

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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