Re: [RESEND Patch 2/2] perf/x86/intel: Add missing branch counters constraint apply

[Peter Zijlstra]

On Sat, Feb 28, 2026 at 01:33:20PM +0800, Dapeng Mi wrote:
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 4768236c054b..4b042d71104f 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -4628,6 +4628,19 @@ static inline void intel_pmu_set_acr_caused_constr(struct perf_event *event,
>  		event->hw.dyn_constraint &= hybrid(event->pmu, acr_cause_mask64);
>  }
>  
> +static inline int intel_set_branch_counter_constr(struct perf_event *event,
> +						  int *num)
> +{
> +	if (branch_sample_call_stack(event))
> +		return -EINVAL;
> +	if (branch_sample_counters(event)) {
> +		(*num)++;
> +		event->hw.dyn_constraint &= x86_pmu.lbr_counters;
> +	}
> +
> +	return 0;
> +}
> +
>  static int intel_pmu_hw_config(struct perf_event *event)
>  {
>  	int ret = x86_pmu_hw_config(event);
> @@ -4698,21 +4711,18 @@ static int intel_pmu_hw_config(struct perf_event *event)
>  		 * group, which requires the extra space to store the counters.
>  		 */
>  		leader = event->group_leader;
> +		if (intel_set_branch_counter_constr(leader, &num))
>  			return -EINVAL;
>  		leader->hw.flags |= PERF_X86_EVENT_BRANCH_COUNTERS;
>  
>  		for_each_sibling_event(sibling, leader) {
> +			if (intel_set_branch_counter_constr(sibling, &num))
> +				return -EINVAL;
> +		}
> +

Do the new bit is this, right?

> +		if (event != leader) {
> +			if (intel_set_branch_counter_constr(event, &num))
>  				return -EINVAL;
>  		}

The point being that for_each_sibling_event() will not have iterated the
event because its not on the list yet?

That wasn't really clear from the changelog and I think that deserves a
comment as well.

Let me go fix that.