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From: Odin Ugedal <>
To: Vincent Guittot <>
Cc: Odin Ugedal <>, Ingo Molnar <>,
	Peter Zijlstra <>,
	Juri Lelli <>,
	Dietmar Eggemann <>,
	Steven Rostedt <>,
	Ben Segall <>, Mel Gorman <>,
	Daniel Bristot de Oliveira <>,
	"open list:CONTROL GROUP (CGROUP)" <>,
	linux-kernel <>
Subject: Re: [PATCH v2] sched/fair: Correctly insert cfs_rq's to list on unthrottle
Date: Thu, 3 Jun 2021 15:12:35 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>


> Out of curiosity, why did you decide to use
> cfs_rq->tg_load_avg_contrib instead of !cfs_rq_is_decayed(cfs_rq)
> which is used to delete the cfs_rq from the list when updating blocked
> load ?

Well, the main reason was that it is currently (without the other in
flight patches) not safe to just use "cfs_rq_is_decayed" directly,
since that could result in
a situation where tg_load_avg_contrib!=0 while
cfs_rq_is_decayed()==true. I guess we can use cfs_rq_is_decayed() if
you prefer that,
and all the other PELT patches are merged. (This was initially why I
thought a new field was a simpler and more elegant solution to make
sure we book-keep correctly,
but when the PELT stuff is fixed properly, that should be no real
issue as long it works as we expect).

I was also thinking about the cfs_rq->nr_running part; is there a
chance of a situation where a cfs_rq->nr_running==1 and it has no
load, resulting in it being decayed and
removed from the list in "__update_blocked_fair"? I have not looked
properly at it, but just wondering if that is actually possible..

Also, out of curiosity, are there some implications of a situation
where tg_load_avg_contrib=0 while *_load!=0, or would that not cause
fairness issues?


  reply	other threads:[~2021-06-03 13:13 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-03 11:38 [PATCH v2] sched/fair: Correctly insert cfs_rq's to list on unthrottle Odin Ugedal
2021-06-03 12:51 ` Vincent Guittot
2021-06-03 13:12   ` Odin Ugedal [this message]
2021-06-03 13:40     ` Vincent Guittot
2021-06-03 13:55       ` Odin Ugedal
2021-06-03 14:39 ` kernel test robot

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