Re: [RFC PATCH 05/31] x86/resctrl: Parse ACPI CMRC table

[Luck, Tony]

On Tue, Aug 04, 2026 at 10:19:26AM -0700, Luck, Tony wrote:
> On Mon, Aug 03, 2026 at 12:03:48AM +0800, Chen Yu wrote:

> >  
> > +/* Scale to bytes for the monitoring counters when ERDT is enabled. */
> > +static int erdt_scale;
> 
> Single value for scale? See below.

Now I've read ahead to patch 9 and see how this is used to set
resctrl_rmid_realloc_threshold. Needs better comments here and
for above erdt_get_scale()
> 
> > +
> >  int erdt_get_max_rmid(void)
> >  {
> >  	return erdt_max_rmid;
> >  }
> >  
> > +int erdt_get_scale(void)
> > +{
> > +	return erdt_scale;
> > +}
> > +
> > +	erdt_scale = max_t(int, erdt_scale, cmrc->up_scale);
> 
> I'd expect that on a machine all CMRC tables would report the same
> up_scale factor. But RDT architecture allows them to be different. Two
> ways to handle this:
> 
> 1) Check that they are all the same. Complain if they are different and
> don't enable cache occupancy events.
> 
> 2) Save the value for each domain and use that value to upscale when
> reporting to user.

I see in patch 9 that you do use this option "2" with "cmrc->up_scale".

> Picking the max value doesn't feel like a good answer.

Given how this is actually used, seems like the best option.
> 
> > +
> > +	return 0;
> > +}
> 
-Tony