Re: [PATCH V2 2/8] perf/x86/intel/uncore: Fix refcnt and other cleanups

[Chen, Zide]

On 6/2/2026 4:52 AM, Mi, Dapeng wrote:
> 
> On 6/2/2026 1:01 AM, Zide Chen wrote:
>> Fix typo UNCORE_BOX_FLAG_INITIATED to UNCORE_BOX_FLAG_INITIALIZED.
>>
>> Rename the 'id' parameter in uncore_box_{ref,unref}() to 'die' to
>> reflect its actual meaning and be consistent with other functions.
>>
>> Remove the incorrect atomic_inc(&box->refcnt) from
>> uncore_pci_pmu_register(): PCI boxes are not tracked by refcnt,
>> and this call incorrectly increments it on a per-die basis.
>>
>> Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
>> ---
>> v2:
>> - Don't rename pmu->activeboxes and keep its semantics because in
>>   uncore_pci_remove() path, uncore_pci_pmu_unregister() won't be
>>   called for non-active boxes.
>> - Since pmu->activeboxes keeps it's name, don't need to rename
>>   box->refcnt to box->cpu_refcnt.
>> ---
>>  arch/x86/events/intel/uncore.c | 11 +++++------
>>  arch/x86/events/intel/uncore.h |  6 +++---
>>  2 files changed, 8 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
>> index b69b6a21d46b..d759888476c3 100644
>> --- a/arch/x86/events/intel/uncore.c
>> +++ b/arch/x86/events/intel/uncore.c
>> @@ -1170,7 +1170,6 @@ static int uncore_pci_pmu_register(struct pci_dev *pdev,
>>  	if (!box)
>>  		return -ENOMEM;
>>  
>> -	atomic_inc(&box->refcnt);
> 
> I'm not sure if we should remove this. The
> uncore_box_ref()/uncore_box_unref() are only called for MSR or MMIO type
> uncore PMUs. For the uncore PMUs of PCI type, the box->refcnt is only
> increased here. All the 3 kinds of uncore PMUs should keep consistent
> behavior on the refcnt. 

box->refcnt tracks how many CPUs are active within this die. Here it is
incorrectly incremented on a per-die basis. Additionally, during the PCI
uncore enumeration or teardown process, there is no per-CPU context, so
box->refcnt is useless in PCI uncore.

PCI uncore only needs pmu->activeboxes.

> Could we keep this and just decrease the refcnt in
> uncore_pci_pmu_unregister()? Thanks.
> 
> 
>>  	box->dieid = die;
>>  	box->pci_dev = pdev;
>>  	box->pmu = pmu;
>> @@ -1518,7 +1517,7 @@ static void uncore_change_context(struct intel_uncore_type **uncores,
>>  		uncore_change_type_ctx(*uncores, old_cpu, new_cpu);
>>  }
>>  
>> -static void uncore_box_unref(struct intel_uncore_type **types, int id)
>> +static void uncore_box_unref(struct intel_uncore_type **types, int die)
>>  {
>>  	struct intel_uncore_type *type;
>>  	struct intel_uncore_pmu *pmu;
>> @@ -1529,7 +1528,7 @@ static void uncore_box_unref(struct intel_uncore_type **types, int id)
>>  		type = *types;
>>  		pmu = type->pmus;
>>  		for (i = 0; i < type->num_boxes; i++, pmu++) {
>> -			box = pmu->boxes[id];
>> +			box = pmu->boxes[die];
>>  			if (box && box->cpu >= 0 && atomic_dec_return(&box->refcnt) == 0)
>>  				uncore_box_exit(box);
>>  		}
>> @@ -1604,14 +1603,14 @@ static int allocate_boxes(struct intel_uncore_type **types,
>>  }
>>  
>>  static int uncore_box_ref(struct intel_uncore_type **types,
>> -			  int id, unsigned int cpu)
>> +			  int die, unsigned int cpu)
>>  {
>>  	struct intel_uncore_type *type;
>>  	struct intel_uncore_pmu *pmu;
>>  	struct intel_uncore_box *box;
>>  	int i, ret;
>>  
>> -	ret = allocate_boxes(types, id, cpu);
>> +	ret = allocate_boxes(types, die, cpu);
>>  	if (ret)
>>  		return ret;
>>  
>> @@ -1619,7 +1618,7 @@ static int uncore_box_ref(struct intel_uncore_type **types,
>>  		type = *types;
>>  		pmu = type->pmus;
>>  		for (i = 0; i < type->num_boxes; i++, pmu++) {
>> -			box = pmu->boxes[id];
>> +			box = pmu->boxes[die];
>>  			if (box && box->cpu >= 0 && atomic_inc_return(&box->refcnt) == 1)
>>  				uncore_box_init(box);
>>  		}
>> diff --git a/arch/x86/events/intel/uncore.h b/arch/x86/events/intel/uncore.h
>> index c2e5ccb1d72c..bad5d8dec8e0 100644
>> --- a/arch/x86/events/intel/uncore.h
>> +++ b/arch/x86/events/intel/uncore.h
>> @@ -185,7 +185,7 @@ struct intel_uncore_box {
>>  #define CFL_UNC_CBO_7_PERFEVTSEL0		0xf70
>>  #define CFL_UNC_CBO_7_PER_CTR0			0xf76
>>  
>> -#define UNCORE_BOX_FLAG_INITIATED		0
>> +#define UNCORE_BOX_FLAG_INITIALIZED		0
>>  /* event config registers are 8-byte apart */
>>  #define UNCORE_BOX_FLAG_CTL_OFFS8		1
>>  /* CFL 8th CBOX has different MSR space */
>> @@ -559,7 +559,7 @@ static inline u64 uncore_read_counter(struct intel_uncore_box *box,
>>  
>>  static inline void uncore_box_init(struct intel_uncore_box *box)
>>  {
>> -	if (!test_and_set_bit(UNCORE_BOX_FLAG_INITIATED, &box->flags)) {
>> +	if (!test_and_set_bit(UNCORE_BOX_FLAG_INITIALIZED, &box->flags)) {
>>  		if (box->pmu->type->ops->init_box)
>>  			box->pmu->type->ops->init_box(box);
>>  	}
>> @@ -567,7 +567,7 @@ static inline void uncore_box_init(struct intel_uncore_box *box)
>>  
>>  static inline void uncore_box_exit(struct intel_uncore_box *box)
>>  {
>> -	if (test_and_clear_bit(UNCORE_BOX_FLAG_INITIATED, &box->flags)) {
>> +	if (test_and_clear_bit(UNCORE_BOX_FLAG_INITIALIZED, &box->flags)) {
>>  		if (box->pmu->type->ops->exit_box)
>>  			box->pmu->type->ops->exit_box(box);
>>  	}