On Thu, 19 Nov 2020 at 12:36, Guilherme G. Piccoli gpiccoli@canonical.com wrote:

On 19/11/2020 05:36, Vincent Guittot wrote:

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On Thu, 19 Nov 2020 at 01:36, Tao Zhou t1zhou@163.com wrote:

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On Thu, Nov 19, 2020 at 07:50:15AM +0800, Tao Zhou wrote:

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

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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.or...

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

[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?

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

Regards, Vincent

Cheers,

Guilherme

Hello Vincent,

sorry to resurrect this thread again, I was trying to backport this patch and corresponding fixes to our Ubuntu 4.15 kernel [1] to fix an issue report by LTP cfs_bandwidth01 test[2], my colleague Guilherme told me there once a discussion about backporting this on this thread.

You mentioned here this should not be backported to earlier stable kernel, I am curious if there is any specific reason of it? Too risky maybe? Thanks! PHLin

[1] https://lists.ubuntu.com/archives/kernel-team/2021-June/121571.html [2] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/sched...

On Thu, Nov 19, 2020 at 9:25 PM Vincent Guittot vincent.guittot@linaro.org wrote:

On Thu, 19 Nov 2020 at 12:36, Guilherme G. Piccoli gpiccoli@canonical.com wrote:

...

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.or...

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

[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?

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

Regards, Vincent

...

Cheers,

Guilherme