Re: [PATCH v7 11/14] mpam,x86/resctrl: Resolve INTEL_PMT_TELEMETRY symbols at runtime

[Luck, Tony]

On Wed, Jun 10, 2026 at 09:21:04AM -0700, Reinette Chatre wrote:
> Hi Tony,
> 
> On 6/10/26 8:49 AM, Luck, Tony wrote:
> > On Wed, Jun 10, 2026 at 08:27:15AM -0700, Reinette Chatre wrote:
> >> On 6/9/26 5:08 PM, Luck, Tony wrote:
> >>> On Mon, Jun 08, 2026 at 04:25:51PM -0700, Reinette Chatre wrote:
> 
> >>>>> +void intel_aet_unmount(void)
> >>>>>  {
> >>>>>  	struct event_group **peg;
> >>>>>  
> >>>>> +	guard(mutex)(&aet_register_lock);
> >>>>
> >>>> Could this get a short-circuit to make behavior on AMD obvious?
> >>>
> >>> Like this?
> >>>
> >>> 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
> >>> 		return;
> >>>
> >>> Same in intel_aet_pre_mount() for symmetry??
> >>
> >> I do not see that this requires to be architecture specific. This capability
> >> introduces AET register()/unregister() and pre_mount()/unmount().
> >> pre_mount() already does no-op if (essentially) nothing is registered. Could
> >> unmount() similarly be a no-op if (essentially) nothing is registered?
> > 
> > Ah, I see. Maybe I just need a better name for my "have_pmt_hold" flag
> > so it can be used as the fast exit indicator in intel_aet_unmount().
> > 
> > Perhaps "pmt_in_use"?
> > 
> > Then:
> > 
> > 	if (!pmt_in_use)
> > 		return;
> 
> Something like this. It is not obvious to me how the rest of unmount will look
> with this.
> Ideally it will be something symmetrical to pre_mount() to make the
> flow and short-circuit of the flow obvious.

With updates applied, mount/umount look like this:

/*
 * Track whether pmt_telemetry enumeration succeeded during mount for use
 * during unmount.
 */
static bool pmt_in_use;

bool intel_aet_pre_mount(void)
{
	bool ret;

	guard(mutex)(&aet_register_lock);
	if (!get_feature || !put_feature)
		return false;

	if (pmt_module) {
		if (!try_module_get(pmt_module))
			return false;
	}

	ret = aet_get_events();

	if (!ret) {
		if (pmt_module)
			module_put(pmt_module);
	} else {
		pmt_in_use = true;
	}

	return ret;
}

void intel_aet_unmount(void)
{
	struct event_group **peg;

	guard(mutex)(&aet_register_lock);
	if (!pmt_in_use)
		return;

	for_each_event_group(peg) {
		if ((*peg)->pfg) {
			struct event_group *e = *peg;

			for (int j = 0; j < e->num_events; j++)
				resctrl_disable_mon_event(e->evts[j].id);
			put_feature((*peg)->pfg);
			(*peg)->pfg = NULL;
		}
	}
	if (pmt_module)
		module_put(pmt_module);
	pmt_in_use = false;
}

}
> 
> Reinette

-Tony