Re: [PATCH 11/20] perf/x86/intel: Setup PEBS constraints base on counter & pdist map

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

On 2025-01-23 9:07 a.m., Dapeng Mi wrote:
> arch-PEBS provides CPUIDs to enumerate which counters support PEBS
> sampling and precise distribution PEBS sampling. Thus PEBS constraints
> can be dynamically configured base on these counter and precise
> distribution bitmap instead of defining them statically.
> 
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> ---
>  arch/x86/events/intel/core.c | 20 ++++++++++++++++++++
>  arch/x86/events/intel/ds.c   |  1 +
>  2 files changed, 21 insertions(+)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 7775e1e1c1e9..0f1be36113fa 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3728,6 +3728,7 @@ intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  			    struct perf_event *event)
>  {
>  	struct event_constraint *c1, *c2;
> +	struct pmu *pmu = event->pmu;
>  
>  	c1 = cpuc->event_constraint[idx];
>  
> @@ -3754,6 +3755,25 @@ intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  		c2->weight = hweight64(c2->idxmsk64);
>  	}
>  
> +	if (x86_pmu.arch_pebs && event->attr.precise_ip) {
> +		u64 pebs_cntrs_mask;
> +		u64 cntrs_mask;
> +
> +		if (event->attr.precise_ip >= 3)
> +			pebs_cntrs_mask = hybrid(pmu, arch_pebs_cap).pdists;
> +		else
> +			pebs_cntrs_mask = hybrid(pmu, arch_pebs_cap).counters;
> +
> +		cntrs_mask = hybrid(pmu, fixed_cntr_mask64) << INTEL_PMC_IDX_FIXED |
> +			     hybrid(pmu, cntr_mask64);
> +
> +		if (pebs_cntrs_mask != cntrs_mask) {
> +			c2 = dyn_constraint(cpuc, c2, idx);
> +			c2->idxmsk64 &= pebs_cntrs_mask;
> +			c2->weight = hweight64(c2->idxmsk64);
> +		}
> +	}

The pebs_cntrs_mask and cntrs_mask wouldn't be changed since the machine
boot. I don't think it's efficient to calculate them every time.

Maybe adding a local pebs_event_constraints_pdist[] and update both
pebs_event_constraints[] and pebs_event_constraints_pdist[] with the
enumerated mask at initialization time.

Update the intel_pebs_constraints() to utilize the corresponding array
according to the precise_ip.

The above may be avoided.

Thanks,
Kan

> +
>  	return c2;
>  }
>  
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index 2f2c6b7c801b..a573ce0e576a 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -2941,6 +2941,7 @@ 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;
>  }
>  
>  /*