Re: [Patch v2 13/24] perf/x86/intel: Update dyn_constranit base on PEBS event precise level

[Mi, Dapeng]

On 2/27/2025 10:06 PM, Liang, Kan wrote:
>
> On 2025-02-18 10:28 a.m., Dapeng Mi wrote:
>> arch-PEBS provides CPUIDs to enumerate which counters support PEBS
>> sampling and precise distribution PEBS sampling. Thus PEBS constraints
>> should be dynamically configured base on these counter and precise
>> distribution bitmap instead of defining them statically.
>>
>> Update event dyn_constraint base on PEBS event precise level.
>>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>> ---
>>  arch/x86/events/intel/core.c | 6 ++++++
>>  arch/x86/events/intel/ds.c   | 1 +
>>  2 files changed, 7 insertions(+)
>>
>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
>> index 472366c3db22..c777e0531d40 100644
>> --- a/arch/x86/events/intel/core.c
>> +++ b/arch/x86/events/intel/core.c
>> @@ -4033,6 +4033,8 @@ static int intel_pmu_hw_config(struct perf_event *event)
>>  		return ret;
>>  
>>  	if (event->attr.precise_ip) {
>> +		struct arch_pebs_cap pebs_cap = hybrid(event->pmu, arch_pebs_cap);
>> +
>>  		if ((event->attr.config & INTEL_ARCH_EVENT_MASK) == INTEL_FIXED_VLBR_EVENT)
>>  			return -EINVAL;
>>  
>> @@ -4046,6 +4048,10 @@ static int intel_pmu_hw_config(struct perf_event *event)
>>  		}
>>  		if (x86_pmu.pebs_aliases)
>>  			x86_pmu.pebs_aliases(event);
>> +
>> +		if (x86_pmu.arch_pebs)
>> +			event->hw.dyn_constraint = event->attr.precise_ip >= 3 ?
>> +						   pebs_cap.pdists : pebs_cap.counters;
>>  	}
> The dyn_constraint is only required when the counter mask is different.
> I think the pebs_cap.counters should be very likely the same as the
> regular counter mask. Maybe something as below (not test).
>
> 	if (x86_pmu.arch_pebs) {
> 		u64 cntr_mask = event->attr.precise_ip >= 3 ?
> 				pebs_cap.pdists : pebs_cap.counters;
> 		if (cntr_mask != hybrid(event->pmu, intel_ctrl))
> 			event->hw.dyn_constraint = cntr_mask;
> 	}

Sure. Thanks.


>
> Thanks,
> Kan
>>  
>>  	if (needs_branch_stack(event)) {
>> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
>> index 519767fc9180..615aefb4e52e 100644
>> --- a/arch/x86/events/intel/ds.c
>> +++ b/arch/x86/events/intel/ds.c
>> @@ -2948,6 +2948,7 @@ static void __init intel_arch_pebs_init(void)
>>  	x86_pmu.pebs_buffer_size = PEBS_BUFFER_SIZE;
>>  	x86_pmu.drain_pebs = intel_pmu_drain_arch_pebs;
>>  	x86_pmu.pebs_capable = ~0ULL;
>> +	x86_pmu.flags |= PMU_FL_PEBS_ALL;
>>  
>>  	x86_pmu.pebs_enable = __intel_pmu_pebs_enable;
>>  	x86_pmu.pebs_disable = __intel_pmu_pebs_disable;
>