linux-kernel - Re: [PATCH V5 2/8] perf/x86: Add PERF_X86_EVENT_NEEDS_BRANCH

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Date:   Mon, 6 Nov 2023 18:12:25 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     kan.liang@...ux.intel.com
Cc:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
        ak@...ux.intel.com, eranian@...gle.com,
        alexey.v.bayduraev@...ux.intel.com, tinghao.zhang@...el.com
Subject: Re: [PATCH V5 2/8] perf/x86: Add PERF_X86_EVENT_NEEDS_BRANCH_STACK
 flag

Em Wed, Oct 25, 2023 at 01:16:20PM -0700, kan.liang@...ux.intel.com escreveu:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> Currently, branch_sample_type !=0 is used to check whether a branch
> stack setup is required. But it doesn't check the sample type,
> unnecessary branch stack setup may be done for a counting event. E.g.,
> perf record -e "{branch-instructions,branch-misses}:S" -j any
> Also, the event only with the new PERF_SAMPLE_BRANCH_COUNTERS branch
> sample type may not require a branch stack setup either.
> 
> Add a new flag NEEDS_BRANCH_STACK to indicate whether the event requires
> a branch stack setup. Replace the needs_branch_stack() by checking the
> new flag.
> 
> The counting event check is implemented here. The later patch will take
> the new PERF_SAMPLE_BRANCH_COUNTERS into account.
> 
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
> 
> No changes since V4

So I saw this on tip/perf/urgent, I'm picking the tools bits then.

- Arnaldo
 
>  arch/x86/events/intel/core.c       | 14 +++++++++++---
>  arch/x86/events/perf_event_flags.h |  1 +
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 41a164764a84..a99449c0d77c 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2527,9 +2527,14 @@ static void intel_pmu_assign_event(struct perf_event *event, int idx)
>  		perf_report_aux_output_id(event, idx);
>  }
>  
> +static __always_inline bool intel_pmu_needs_branch_stack(struct perf_event *event)
> +{
> +	return event->hw.flags & PERF_X86_EVENT_NEEDS_BRANCH_STACK;
> +}
> +
>  static void intel_pmu_del_event(struct perf_event *event)
>  {
> -	if (needs_branch_stack(event))
> +	if (intel_pmu_needs_branch_stack(event))
>  		intel_pmu_lbr_del(event);
>  	if (event->attr.precise_ip)
>  		intel_pmu_pebs_del(event);
> @@ -2820,7 +2825,7 @@ static void intel_pmu_add_event(struct perf_event *event)
>  {
>  	if (event->attr.precise_ip)
>  		intel_pmu_pebs_add(event);
> -	if (needs_branch_stack(event))
> +	if (intel_pmu_needs_branch_stack(event))
>  		intel_pmu_lbr_add(event);
>  }
>  
> @@ -3897,7 +3902,10 @@ static int intel_pmu_hw_config(struct perf_event *event)
>  			x86_pmu.pebs_aliases(event);
>  	}
>  
> -	if (needs_branch_stack(event)) {
> +	if (needs_branch_stack(event) && is_sampling_event(event))
> +		event->hw.flags  |= PERF_X86_EVENT_NEEDS_BRANCH_STACK;
> +
> +	if (intel_pmu_needs_branch_stack(event)) {
>  		ret = intel_pmu_setup_lbr_filter(event);
>  		if (ret)
>  			return ret;
> diff --git a/arch/x86/events/perf_event_flags.h b/arch/x86/events/perf_event_flags.h
> index 1dc19b9b4426..a1685981c520 100644
> --- a/arch/x86/events/perf_event_flags.h
> +++ b/arch/x86/events/perf_event_flags.h
> @@ -20,3 +20,4 @@ PERF_ARCH(TOPDOWN,		0x04000) /* Count Topdown slots/metrics events */
>  PERF_ARCH(PEBS_STLAT,		0x08000) /* st+stlat data address sampling */
>  PERF_ARCH(AMD_BRS,		0x10000) /* AMD Branch Sampling */
>  PERF_ARCH(PEBS_LAT_HYBRID,	0x20000) /* ld and st lat for hybrid */
> +PERF_ARCH(NEEDS_BRANCH_STACK,	0x40000) /* require branch stack setup */
> -- 
> 2.35.1
> 

-- 

- Arnaldo