Re: [PATCH V5 2/8] perf/x86: Add PERF_X86_EVENT_NEEDS_BRANCH_STACK flag

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

On 2023-11-06 4:12 p.m., Arnaldo Carvalho de Melo wrote:
> Em Wed, Oct 25, 2023 at 01:16:20PM -0700, kan.liang@linux.intel.com escreveu:
>> From: Kan Liang <kan.liang@linux.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@linux.intel.com>
>> ---
>>
>> No changes since V4
> 
> So I saw this on tip/perf/urgent, I'm picking the tools bits then.

Thanks Arnaldo.

Ian has already reviewed the tool parts.

But I still owe a test case for the feature. I will post a patch later.
https://lore.kernel.org/lkml/acbb895a-475e-4679-98fc-6b90c05a00af@linux.intel.com/

Thanks,
Kan

> 
> - 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
>>
>