Re: [EXT] Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs

[Alex Belits]

On 1/29/21 06:23, Marcelo Tosatti wrote:
> External Email
>
> ----------------------------------------------------------------------
> On Fri, Jan 29, 2021 at 08:55:20AM -0500, Nitesh Narayan Lal wrote:
> > On 1/28/21 3:01 PM, Thomas Gleixner wrote:
> > > On Thu, Jan 28 2021 at 13:59, Marcelo Tosatti wrote:
> > > > > The whole pile wants to be reverted. It's simply broken in several ways.
> > > > I was asking for your comments on interaction with CPU hotplug :-)
> > > Which I answered in an seperate mail :)
> > >
> > > > So housekeeping_cpumask has multiple meanings. In this case:
> > > ...
> > >
> > > > So as long as the meaning of the flags are respected, seems
> > > > alright.
> > > Yes. Stuff like the managed interrupts preference for housekeeping CPUs
> > > when a affinity mask spawns housekeeping and isolated is perfectly
> > > fine. It's well thought out and has no limitations.
> > >
> > > > Nitesh, is there anything preventing this from being fixed
> > > > in userspace ? (as Thomas suggested previously).
> > > Everything with is not managed can be steered by user space.
> > >
> > > Thanks,
> > >
> > >          tglx
> >
> > So, I think the conclusion here would be to revert the change made in
> > cpumask_local_spread via the patch:
> >   - lib: Restrict cpumask_local_spread to housekeeping CPUs
> >
> > Also, a similar case can be made for the rps patch that went in with
> > this:
> >  - net: Restrict receive packets queuing to housekeeping CPUs
>
> Yes, this is the userspace solution:
>
> https://lkml.org/lkml/2021/1/22/815
>
> Should have a kernel document with this info and examples
> (the network queue configuration as well). Will
> send something.
>
> >  + net: accept an empty mask in /sys/class/net/*/queues/rx-*/rps_cpus
> >
> > I am not sure about the PCI patch as I don't think we can control that from
> > the userspace or maybe I am wrong?
>
> You mean "lib: Restrict cpumask_local_spread to housekeeping CPUs" ?

If we want to do it from userspace, we should have something that 
triggers it in userspace. Should we use udev for this purpose?

--
Alex