Re: [PATCH V2 6/8] perf/x86/intel/uncore: Introduce PMU flags and broken state

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 6/2/2026 1:01 AM, Zide Chen wrote:
> Replace the boolean 'registered' field in intel_uncore_pmu with an
> unsigned long 'flags' field, and add a PMU_BROKEN flag to track box
> setup failures. Broken flag is sticky, means it won't be cleared
> unless module reload or system reboot.
>
> Broken PMUs are skipped in the CPU hotplug and box allocation paths.
>
> When any box fails to initialize, the PMU is marked broken.  Broken
> PMUs reject new event assignments and skip future box setup attempts.
> If the PMU was already registered, it remains so to avoid disrupting
> in-flight events on other boxes.
>
> Signed-off-by: Zide Chen <zide.chen@intel.com>
> ---
> v2:
> - Make the broken flag sticky by clear_bit() in uncore_pmu_unregister()
> other than zeroing out pmu->flag.
> - In uncore_change_type_ctx(), don't stop CPU migration on broken PMU
>   for in-flight events.  (Sashiko).
> - Use box->cpu == -1 to identify inactive boxes that don't need
>   migration, no need to check uncore_die_has_box(), which is incomplete.
> ---
>  arch/x86/events/intel/uncore.c     | 44 ++++++++++++++++++++++--------
>  arch/x86/events/intel/uncore.h     | 13 ++++++++-
>  arch/x86/events/intel/uncore_snb.c |  2 +-
>  3 files changed, 46 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
> index 283e41933ba7..f2cb3fde2dda 100644
> --- a/arch/x86/events/intel/uncore.c
> +++ b/arch/x86/events/intel/uncore.c
> @@ -757,7 +757,7 @@ static int uncore_pmu_event_init(struct perf_event *event)
>  
>  	pmu = uncore_event_to_pmu(event);
>  	/* no device found for this pmu */
> -	if (!pmu->registered)
> +	if (!uncore_pmu_available(pmu))
>  		return -ENOENT;
>  
>  	/* Sampling not supported yet */
> @@ -953,16 +953,18 @@ static int uncore_pmu_register(struct intel_uncore_pmu *pmu)
>  
>  	ret = perf_pmu_register(&pmu->pmu, pmu->name, -1);
>  	if (!ret)
> -		pmu->registered = true;
> +		uncore_pmu_set_registered(pmu);
>  	return ret;
>  }
>  
>  static void uncore_pmu_unregister(struct intel_uncore_pmu *pmu)
>  {
> -	if (!pmu->registered)
> +	if (!uncore_pmu_registered(pmu))
>  		return;
>  	perf_pmu_unregister(&pmu->pmu);
> -	pmu->registered = false;
> +
> +	/* Keep PMU_BROKEN_BIT stick. */
> +	uncore_pmu_clear_registered(pmu);

Why to set PMU_BROKEN_BIT to a stick bit and doesn't clear it when
unregistering the PMU? Per my understanding, there is no active boxes when
uncore_pmu_unregister() is called, seem all flags can be cleared. When the
new CPU or PCI device are hot plug-in again, it may be a new device or the
old issue which leads to the PMU can't be initialized has been fixed, the
uncore PMU can work correctly, the PMU_BROKEN_BIT should be set any more.


>  }
>  
>  static void uncore_free_boxes(struct intel_uncore_pmu *pmu)
> @@ -1153,7 +1155,12 @@ static int uncore_box_setup(struct intel_uncore_pmu *pmu,
>  {
>  	int ret;
>  
> -	uncore_box_init(box);
> +	if (uncore_pmu_broken(pmu))
> +		return -ENODEV;
> +
> +	ret = uncore_box_init(box);
> +	if (ret)
> +		goto err;
>  
>  	/* First active box registers the pmu. */
>  	if (atomic_inc_return(&pmu->activeboxes) > 1)
> @@ -1167,6 +1174,16 @@ static int uncore_box_setup(struct intel_uncore_pmu *pmu,
>  
>  	return 0;
>  err:
> +	/*
> +	 * On failure on any box, mark the per-package PMU as broken regardless
> +	 * of whether it was registered or not.
> +	 *
> +	 * Don't decrement refcnt to avoid other in-die CPUs from trying to set
> +	 * up the PMU box again.
> +	 *
> +	 * Don't kfree box; MSR and MMIO boxes are freed at module exit only.
> +	 */
> +	uncore_pmu_set_broken(pmu);
>  	uncore_box_exit(box);
>  	return ret;
>  }
> @@ -1190,8 +1207,10 @@ static int uncore_pci_pmu_register(struct pci_dev *pdev,
>  		return -EINVAL;
>  
>  	box = uncore_alloc_box(type, NUMA_NO_NODE);
> -	if (!box)
> +	if (!box) {
> +		uncore_pmu_set_broken(pmu);
>  		return -ENOMEM;
> +	}
>  
>  	box->dieid = die;
>  	box->pci_dev = pdev;
> @@ -1504,7 +1523,8 @@ static void uncore_change_type_ctx(struct intel_uncore_type *type, int old_cpu,
>  
>  		if (old_cpu < 0) {
>  			WARN_ON_ONCE(box->cpu != -1);
> -			if (uncore_die_has_box(type, die, pmu->pmu_idx)) {
> +			if (uncore_die_has_box(type, die, pmu->pmu_idx) &&
> +			    !uncore_pmu_broken(pmu)) {
>  				box->cpu = new_cpu;
>  				cpumask_set_cpu(new_cpu, &pmu->cpu_mask);
>  			}
> @@ -1512,12 +1532,14 @@ static void uncore_change_type_ctx(struct intel_uncore_type *type, int old_cpu,
>  		}
>  
>  		WARN_ON_ONCE(box->cpu != -1 && box->cpu != old_cpu);
> -		box->cpu = -1;
>  		cpumask_clear_cpu(old_cpu, &pmu->cpu_mask);
> -		if (new_cpu < 0)
> +		if (new_cpu < 0) {
> +			box->cpu = -1;
>  			continue;
> +		}
>  
> -		if (!uncore_die_has_box(type, die, pmu->pmu_idx))
> +		/* non-active box doesn't need migration. */
> +		if (box->cpu == -1)
>  			continue;
>  		uncore_pmu_cancel_hrtimer(box);
>  		perf_pmu_migrate_context(&pmu->pmu, old_cpu, new_cpu);
> @@ -1593,7 +1615,7 @@ static int allocate_boxes(struct intel_uncore_type **types,
>  		type = *types;
>  		pmu = type->pmus;
>  		for (i = 0; i < type->num_boxes; i++, pmu++) {

IIUC, the "type->num_boxes" actually indicates the number of PMU  or the
number of box classes. Since currently there could be multiple boxes for
each kind of PMUs on the multiple dies device, the name "num_boxes" become
inaccurate and much misleading. could we change it to a more accurate name,
like "num_pmus" or "num_box_classes"?


> -			if (pmu->boxes[die])
> +			if (pmu->boxes[die] || uncore_pmu_broken(pmu))
>  				continue;
>  			box = uncore_alloc_box(type, cpu_to_node(cpu));
>  			if (!box)
> diff --git a/arch/x86/events/intel/uncore.h b/arch/x86/events/intel/uncore.h
> index d732b87be0a9..0adb477d9708 100644
> --- a/arch/x86/events/intel/uncore.h
> +++ b/arch/x86/events/intel/uncore.h
> @@ -146,13 +146,24 @@ struct intel_uncore_pmu {
>  	struct pmu			pmu;
>  	char				name[UNCORE_PMU_NAME_LEN];
>  	int				pmu_idx;
> -	bool				registered;
> +	unsigned long			flags;
>  	atomic_t			activeboxes;
>  	cpumask_t			cpu_mask;
>  	struct intel_uncore_type	*type;
>  	struct intel_uncore_box		**boxes;
>  };
>  
> +#define PMU_REGISTERED_BIT	0
> +#define PMU_BROKEN_BIT		1
> +
> +#define uncore_pmu_registered(pmu)	test_bit(PMU_REGISTERED_BIT, &(pmu)->flags)
> +#define uncore_pmu_broken(pmu)		test_bit(PMU_BROKEN_BIT, &(pmu)->flags)
> +#define uncore_pmu_available(pmu)	(uncore_pmu_registered(pmu) &&  \
> +					 !uncore_pmu_broken(pmu))
> +#define uncore_pmu_set_registered(pmu)	set_bit(PMU_REGISTERED_BIT, &(pmu)->flags)
> +#define uncore_pmu_set_broken(pmu)	set_bit(PMU_BROKEN_BIT, &(pmu)->flags)
> +#define uncore_pmu_clear_registered(pmu) clear_bit(PMU_REGISTERED_BIT, &(pmu)->flags)
> +
>  struct intel_uncore_extra_reg {
>  	raw_spinlock_t lock;
>  	u64 config, config1, config2;
> diff --git a/arch/x86/events/intel/uncore_snb.c b/arch/x86/events/intel/uncore_snb.c
> index c5347920541c..055131c508ff 100644
> --- a/arch/x86/events/intel/uncore_snb.c
> +++ b/arch/x86/events/intel/uncore_snb.c
> @@ -940,7 +940,7 @@ static int snb_uncore_imc_event_init(struct perf_event *event)
>  
>  	pmu = uncore_event_to_pmu(event);
>  	/* no device found for this pmu */
> -	if (!pmu->registered)
> +	if (!uncore_pmu_available(pmu))
>  		return -ENOENT;
>  
>  	/* Sampling not supported yet */