RE: [PATCH v11 10/23] x86/resctrl: Remove MSR reading of event configuration value

[Luck, Tony]

> >> This new arch API has sharp corners because of asymmetry of where resctrl
> >> runs the arch function. I do not think it is required to change this since we
> >> can only speculate about how this may be used in the future but I do think
> >> it will be helpful to add comments that highlight:
> >>
> >> resctrl_arch_mon_event_config_get() ->  May run on CPU that does not belong to domain.
> >> resctrl_arch_mon_event_config_set() ->  Runs on CPU that belongs to domain.
> >
> > Here's a vague data point about the future to help with speculation.
> >
> > I have something coming along the pipeline that also can run on any CPU.
> >
> > I am contemplating a flag in the rdt_resource structure (in appropriate substructure
> > resctrl_cache/resctrl_membw) to indicate "domain" vs. "any" for operations.
> >
> > Would something like that be useful here?
>
> hmm ... I cannot envision how this may look. Could you please elaborate?
>
> You mention "a" (singular) flag in rdt_resource while this scenario involves
> different ops having different scope. This makes me think that this flag may
> have to be per operation that in turn would need additional infrastructure to
> manage and track operations.
>
> These "arch" functions are evolving as the work to support MPAM is done and
> so far I think it has been quite ad-hoc to just refactor arch specific code
> into "arch" helpers instead of keeping track of which scope they are running in.
> This currently requires any arch implementing an "arch" helper to be well aware
> of how resctrl will call it.

Reinette,

I haven't fleshed it out yet. One option would be to have a "choose_cpu_mask()"
function that takes resource and domain parameters (and given your comment
about this case an operation code). Then use that as the mask in an smp_call*().

Operations that can run anywhere would return a mask with just bit for the
current CPU. Those tied to a domain, a copy of the domain mask.

-Tony