linux-kernel - Re: [PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs

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Message-ID: <17fc60a3-cc50-7cff-eb46-904c2f0c416e@canonical.com>
Date:   Wed, 18 Nov 2020 19:56:38 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...onical.com>
To:     vincent.guittot@...aro.org
Cc:     bsegall@...gle.com, dietmar.eggemann@....com,
        juri.lelli@...hat.com, zohooouoto@...o.com.cn, mgorman@...e.de,
        mingo@...hat.com, ouwen210@...mail.com, pauld@...hat.com,
        peterz@...radead.org, pkondeti@...eaurora.org, rostedt@...dmis.org,
        Jay Vosburgh <jay.vosburgh@...onical.com>,
        Gavin Guo <gavin.guo@...onical.com>, halves@...onical.com,
        nivedita.singhvi@...onical.com, linux-kernel@...r.kernel.org,
        gpiccoli@...onical.com
Subject: Re: [PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list

Hi Vincent (and all CCed), I'm sorry to ping about such "old" patch, but
we experienced a similar condition to what this patch addresses; it's an
older kernel (4.15.x) but when suggesting the users to move to an
updated 5.4.x kernel, we noticed that this patch is not there, although
similar ones are (like [0] and [1]).

So, I'd like to ask if there's any particular reason to not backport
this fix to stable kernels, specially the longterm 5.4. The main reason
behind the question is that the code is very complex for non-experienced
scheduler developers, and I'm afraid in suggesting such backport to 5.4
and introduce complex-to-debug issues.

Let me know your thoughts Vincent (and all CCed), thanks in advance.
Cheers,

Guilherme

P.S. For those that deleted this thread from the email client, here's a
link:
https://lore.kernel.org/lkml/20200513135528.4742-1-vincent.guittot@linaro.org/

[0]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fe61468b2cb

[1]
https://lore.kernel.org/lkml/20200506141821.GA9773@lorien.usersys.redhat.com/
<- great thread BTW!