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

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Message-ID: <20201118233039.GA6015@geo.homenetwork>
Date:   Thu, 19 Nov 2020 07:30:39 +0800
From:   Tao Zhou <t1zhou@....com>
To:     "Guilherme G. Piccoli" <gpiccoli@...onical.com>
Cc:     vincent.guittot@...aro.org, 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,
        t1zhou@....com
Subject: Re: [PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list

Hi Guilherme,

On Wed, Nov 18, 2020 at 07:56:38PM -0300, Guilherme G. Piccoli wrote:
> 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!

Backport this patch to 5.4 need runnable_avg. but it is not introduced in 5.4
that time(please correct me if I am wrong).


Thanks,
Tao