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

["gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>]

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

thanks,

greg k-h