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

["Liang, Kan" <kan.liang@linux.intel.com>]

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@linux.intel.com>
> ---
>  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;
	}


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;