Since telemetry events are enumerated on resctrl mount the RDT_RESOURCE_PERF_PKG
resource is not considered "monitoring capable" during early resctrl initialization.
This means that the domain list for RDT_RESOURCE_PERF_PKG is not built when the CPU
hot plug notifiers are registered and run for the first time right after resctrl
initialization.

Mark the RDT_RESOURCE_PERF_PKG as "monitoring capable" upon successful telemetry event
enumeration to ensure future CPU hotplug events include this resource and initialize its
domain list for CPUs that are already online.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/resctrl/core.c      | 16 +++++++++++++++-
 arch/x86/kernel/cpu/resctrl/intel_aet.c |  2 ++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 955a1904ba2a..2d8c20819ec3 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -761,14 +761,28 @@ static int resctrl_arch_offline_cpu(unsigned int cpu)
 
 void resctrl_arch_pre_mount(void)
 {
+	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_PERF_PKG].r_resctrl;
 	static atomic_t only_once = ATOMIC_INIT(0);
-	int old = 0;
+	int cpu, old = 0;
 
 	if (!atomic_try_cmpxchg(&only_once, &old, 1))
 		return;
 
 	if (!intel_aet_get_events())
 		return;
+
+	/*
+	 * Late discovery of telemetry events means the domains for the
+	 * resource were not built. Do that now.
+	 */
+	cpus_read_lock();
+	mutex_lock(&domain_list_lock);
+	r->mon_capable = true;
+	rdt_mon_capable = true;
+	for_each_online_cpu(cpu)
+		domain_add_cpu_mon(cpu, r);
+	mutex_unlock(&domain_list_lock);
+	cpus_read_unlock();
 }
 
 enum {
diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
index 03d159afcfe1..bc0a4d84a4e0 100644
--- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
+++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
@@ -225,6 +225,8 @@ static bool enable_events(struct event_group *e, struct pmt_feature_group *p)
 		resctrl_enable_mon_event(e->evts[j].id, true,
 					 e->evts[j].bin_bits, &e->evts[j]);
 
+	pr_info("%s %s monitoring detected\n", r->name, e->name);
+
 	return true;
 }
 
-- 
2.51.0

Hi Tony,

On 10/13/25 3:33 PM, Tony Luck wrote:

> diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> index 03d159afcfe1..bc0a4d84a4e0 100644
> --- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
> +++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> @@ -225,6 +225,8 @@ static bool enable_events(struct event_group *e, struct pmt_feature_group *p)
>  		resctrl_enable_mon_event(e->evts[j].id, true,
>  					 e->evts[j].bin_bits, &e->evts[j]);
>  
> +	pr_info("%s %s monitoring detected\n", r->name, e->name);
> +
>  	return true;
>  }
>  

Is this a stray hunk? It seems unrelated to what the changelog describes.

reinette