Re: [PATCH] x86/resctrl: Don't try to free nonexistent RMIDs

Dave Martin
2024-06-18T16:16:57Z

Hi Reinette,

On Tue, Jun 18, 2024 at 08:43:51AM -0700, Reinette Chatre wrote:
> Hi Dave,
>
> On 6/18/24 2:30 AM, Dave Martin wrote:
> > On Mon, Jun 17, 2024 at 08:53:38AM -0700, Reinette Chatre wrote:
> > > On 6/17/24 4:55 AM, Dave Martin wrote:
>
> > > > As it happens I tested with rdt=cmt,mbmtotal,mbmlocal,l3cat,l3cdp
> > > > (though I made no effort to exercise these features other than running
> > > > the selftests). I can note this in the commit if you prefer.
> > >
> > > hmmm ... those parameters should not be necessary unless the system
> > > has those features forced off by default because of errata. Doing
> > > functional testing on these systems via such enabling is fine
> > > though.
> > >
> > > Reinette
> >
> > I got these kernel args from James. Apparently some of these features
> > are defaulted to off by the firmware on the box I'm using, but we're not
> > sure why. I haven't dug into it.
>
> resctrl does not provide capability to override features that the hardware
> does not advertise as supporting. resctrl does sometimes force hardware
> advertised features off because of errata (for example, see [1]) and the
> kernel "rdt=" parameter can be used to override that. This same option also
> enables administrators to ignore some features on their platforms.
>
> Reinette
>
> [1] https://lore.kernel.org/all/3aea0a3bae219062c812668bd9b7b8f1a25003ba.1503512900.git.tony.luck@intel.com/

Possibly the box in question falls under this case. I'll need to check
with James and/or experiment.

Either way, I don't think this impacts the tested-ness of this patch,
but please shout if you have concerns.

Cheers
---Dave