Re: [Patch v5 10/18] perf/x86/intel: Allow LBR read helpers to operate on explicit stacks

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Oct 29, 2026 at 12:39:06PM +0800, Dapeng Mi wrote:
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index ee724b28d90c..63f0504f9d2a 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -105,7 +105,10 @@
>  
>  #define ARCH_LBR_CTL_MASK			0x7f000e
>  
> -static void intel_pmu_lbr_filter(struct cpu_hw_events *cpuc);
> +static void intel_pmu_lbr_filter(struct cpu_hw_events *cpuc,
> +				 struct perf_branch_stack *lbr_stack,
> +				 struct perf_branch_entry *lbr_entries,
> +				 u64 *lbr_counters);
>  
>  static __always_inline bool is_lbr_call_stack_bit_set(u64 config)
>  {
> @@ -741,10 +744,12 @@ void intel_pmu_lbr_disable_all(void)
>  	}
>  }
>  
> -void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc)
> +void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc,
> +			   struct perf_branch_stack *lbr_stack,
> +			   struct perf_branch_entry *lbr_entries)
>  {
>  	unsigned long mask = x86_pmu.lbr_nr - 1;
> -	struct perf_branch_entry *br = cpuc->lbr_entries;
> +	struct perf_branch_entry *br = lbr_entries;
>  	u64 tos = intel_pmu_lbr_tos();
>  	int i;
>  
> @@ -775,11 +780,13 @@ void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc)
>   * is the same as the linear address, allowing us to merge the LIP and EIP
>   * LBR formats.
>   */
> -void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)
> +void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc,
> +			   struct perf_branch_stack *lbr_stack,
> +			   struct perf_branch_entry *lbr_entries)
>  {
>  	bool need_info = false, call_stack = false;
>  	unsigned long mask = x86_pmu.lbr_nr - 1;
> -	struct perf_branch_entry *br = cpuc->lbr_entries;
> +	struct perf_branch_entry *br = lbr_entries;
>  	u64 tos = intel_pmu_lbr_tos();
>  	int i;
>  	int out = 0;

This makes no sense; why do you keep passing lbr_entries around when we
have lbr_stack.entries[] ?