linux-kernel - Re: [PATCH 6.1 0/2] io_uring/io-wq: respect cgroup cpusets

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Message-ID: <f588a1dc-590f-46aa-8d0c-ac792606c662@kernel.dk>
Date: Tue, 1 Oct 2024 07:35:32 -0600
From: Jens Axboe <axboe@...nel.dk>
To: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
 "MOESSBAUER, Felix" <felix.moessbauer@...mens.com>
Cc: "Schmidt, Adriaan" <adriaan.schmidt@...mens.com>,
 "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
 "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
 "Bezdeka, Florian" <florian.bezdeka@...mens.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "longman@...hat.com" <longman@...hat.com>,
 "asml.silence@...il.com" <asml.silence@...il.com>,
 "stable@...r.kernel.org" <stable@...r.kernel.org>,
 "dqminh@...udflare.com" <dqminh@...udflare.com>
Subject: Re: [PATCH 6.1 0/2] io_uring/io-wq: respect cgroup cpusets

On 10/1/24 1:50 AM, gregkh@...uxfoundation.org wrote:
> On Tue, Oct 01, 2024 at 07:32:42AM +0000, MOESSBAUER, Felix wrote:
>> On Mon, 2024-09-30 at 21:15 +0200, Greg KH wrote:
>>> On Wed, Sep 11, 2024 at 06:23:14PM +0200, Felix Moessbauer wrote:
>>>> Hi,
>>>>
>>>> as discussed in [1], this is a manual backport of the remaining two
>>>> patches to let the io worker threads respect the affinites defined
>>>> by
>>>> the cgroup of the process.
>>>>
>>>> In 6.1 one worker is created per NUMA node, while in da64d6db3bd3
>>>> ("io_uring: One wqe per wq") this is changed to only have a single
>>>> worker.
>>>> As this patch is pretty invasive, Jens and me agreed to not
>>>> backport it.
>>>>
>>>> Instead we now limit the workers cpuset to the cpus that are in the
>>>> intersection between what the cgroup allows and what the NUMA node
>>>> has.
>>>> This leaves the question what to do in case the intersection is
>>>> empty:
>>>> To be backwarts compatible, we allow this case, but restrict the
>>>> cpumask
>>>> of the poller to the cpuset defined by the cgroup. We further
>>>> believe
>>>> this is a reasonable decision, as da64d6db3bd3 drops the NUMA
>>>> awareness
>>>> anyways.
>>>>
>>>> [1]
>>>> https://lore.kernel.org/lkml/ec01745a-b102-4f6e-abc9-abd636d36319@kernel.dk
>>>
>>> Why was neither of these actually tagged for inclusion in a stable
>>> tree?
>>
>> This is a manual backport of these patches for 6.1, as the subsystem
>> changed significantly between 6.1 and 6.2, making an automated backport
>> impossible. This has been agreed on with Jens in
>> https://lore.kernel.org/lkml/ec01745a-b102-4f6e-abc9-abd636d36319@kernel.dk/
>>
>>> Why just 6.1.y?  Please submit them for all relevent kernel versions.
>>
>> The original patch was tagged stable and got accepted in 6.6, 6.10 and
>> 6.11.
> 
> No they were not at all.  Please properly tag them in the future as per
> the documentation if you wish to have things applied to the stable
> trees:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

That's my bad, missed that one of them did not get marked for stable,
the sqpoll one did.

-- 
Jens Axboe