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Subject: Re: [PATCH v3] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list
To:     Vincent Guittot <vincent.guittot@linaro.org>,
        Tao Zhou <t1zhou@163.com>
Cc:     "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        Sasha Levin <sashal@kernel.org>,
        SeongJae Park <sjpark@amazon.com>,
        Ben Segall <bsegall@google.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Tao Zhou <zohooouoto@zoho.com.cn>,
        Mel Gorman <mgorman@suse.de>, Ingo Molnar <mingo@redhat.com>,
        Tao Zhou <ouwen210@hotmail.com>, Phil Auld <pauld@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Pavan Kondeti <pkondeti@codeaurora.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Jay Vosburgh <jay.vosburgh@canonical.com>,
        Gavin Guo <gavin.guo@canonical.com>, halves@canonical.com,
        nivedita.singhvi@canonical.com,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "# v4 . 16+" <stable@vger.kernel.org>
References: <17fc60a3-cc50-7cff-eb46-904c2f0c416e@canonical.com>
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 <CAKfTPtBYm8UtBBnbc7qddA2_OAa3vwH=KoHNgvsQJ9zO2KocYQ@mail.gmail.com>
From:   "Guilherme G. Piccoli" <gpiccoli@canonical.com>
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Message-ID: <7c9462c9-8908-8592-0727-9117d4173724@canonical.com>
Date:   Thu, 19 Nov 2020 08:34:46 -0300
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On 19/11/2020 05:36, Vincent Guittot wrote:
> On Thu, 19 Nov 2020 at 01:36, Tao Zhou <t1zhou@163.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@hotmail.com' and 'zohooouoto@zoho.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?
Cheers,


Guilherme