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

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Date:   Thu, 19 Nov 2020 14:25:05 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     "Guilherme G. Piccoli" <gpiccoli@...onical.com>
Cc:     Tao Zhou <t1zhou@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>,
        SeongJae Park <sjpark@...zon.com>,
        Ben Segall <bsegall@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Tao Zhou <zohooouoto@...o.com.cn>,
        Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
        Tao Zhou <ouwen210@...mail.com>, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jay Vosburgh <jay.vosburgh@...onical.com>,
        Gavin Guo <gavin.guo@...onical.com>, halves@...onical.com,
        nivedita.singhvi@...onical.com,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "# v4 . 16+" <stable@...r.kernel.org>
Subject: Re: [PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list

On Thu, 19 Nov 2020 at 12:36, Guilherme G. Piccoli
<gpiccoli@...onical.com> wrote:
>
>
>
> On 19/11/2020 05:36, Vincent Guittot wrote:
> > On Thu, 19 Nov 2020 at 01:36, Tao Zhou <t1zhou@....com> wrote:
> >>
> >> On Thu, Nov 19, 2020 at 07:50:15AM +0800, Tao Zhou wrote:
> >>> 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!
> >>>
> >>> 'sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_rq list" failed to apply to
> >>> 5.4-stable tree'
> >>>
> >>> You could check above. But I do not have the link about this. Can't search it
> >>> on LKML web: https://lore.kernel.org/lkml/
> >>>
> >>> BTW: 'ouwen210@...mail.com' and 'zohooouoto@...o.com.cn' all is myself.
> >>>
> >>> Sorry for the confusing..
> >>>
> >>> Thanks.
> >>
> >> Sorry again. I forget something. It is in the stable.
> >>
> >> Here it is:
> >>
> >>   https://lore.kernel.org/stable/159041776924279@kroah.com/
> >
> > I think it has never been applied to stable.
> > As you mentioned, the backport has been sent :
> > https://lore.kernel.org/stable/20200525172709.GB7427@vingu-book/
> >
> > I received another emailed in September and pointed out to the
> > backport : https://www.spinics.net/lists/stable/msg410445.html
> >
> >
> >>
>
> Thanks a lot Tao and Vincent! Nice to know that you already worked the
> backport, gives much more confidence when the author does that heheh
>
> So, this should go to stable 5.4.y, but not 4.19.y IIUC?

Yeah. they should be backported up to v5.1 but not earlier

Regards,
Vincent

> Cheers,
>
>
> Guilherme