Re: [Patch v9 10/12] perf/x86/intel: Update dyn_constranit base on PEBS event precise level

[Mi, Dapeng]

On 11/6/2025 10:52 PM, Peter Zijlstra wrote:
> On Wed, Oct 29, 2025 at 06:21:34PM +0800, 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.
> What happened to this:
>
>   https://lore.kernel.org/all/e0b25b3e-aec0-4c43-9ab2-907186b56c71@xxxxxxxxxxxxxxx/

About the issue, Kan ever posted a patch to mitigate the risk, but it seems
the patch is not merged yet.

https://lore.kernel.org/all/20250512175542.2000708-1-kan.liang@xxxxxxxxxxxxxxx/


>
>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>> ---
>>  arch/x86/events/intel/core.c | 11 +++++++++++
>>  arch/x86/events/intel/ds.c   |  1 +
>>  2 files changed, 12 insertions(+)
>>
>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
>> index 6e04d73dfae5..40ccfd80d554 100644
>> --- a/arch/x86/events/intel/core.c
>> +++ b/arch/x86/events/intel/core.c
>> @@ -4252,6 +4252,8 @@ static int intel_pmu_hw_config(struct perf_event *event)
>>  	}
>>  
>>  	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;
>>  
>> @@ -4265,6 +4267,15 @@ 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) {
>> +			u64 cntr_mask = hybrid(event->pmu, intel_ctrl) &
>> +						~GLOBAL_CTRL_EN_PERF_METRICS;
>> +			u64 pebs_mask = event->attr.precise_ip >= 3 ?
>> +						pebs_cap.pdists : pebs_cap.counters;
>> +			if (cntr_mask != pebs_mask)
>> +				event->hw.dyn_constraint &= pebs_mask;
>> +		}
>>  	}
>>  
>>  	if (needs_branch_stack(event)) {
>> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
>> index 5c26a5235f94..1179980f795b 100644
>> --- a/arch/x86/events/intel/ds.c
>> +++ b/arch/x86/events/intel/ds.c
>> @@ -3005,6 +3005,7 @@ 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;
>> -- 
>> 2.34.1
>>