Re: [PATCH 3/6] perf: Use sample_flags for branch stack

[Namhyung Kim]

On Wed, Aug 31, 2022 at 07:55:11AM -0700, kan.liang@xxxxxxxxxxxxxxx wrote:
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> 
> Use the new sample_flags to indicate whether the branch stack is filled
> by the PMU driver.
> 
> Remove the br_stack from the perf_sample_data_init() to minimize the number
> of cache lines touched.
> 
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> ---
>  arch/powerpc/perf/core-book3s.c | 1 +
>  arch/x86/events/core.c          | 4 +++-
>  arch/x86/events/intel/core.c    | 4 +++-
>  arch/x86/events/intel/ds.c      | 5 ++++-
>  include/linux/perf_event.h      | 4 ++--
>  kernel/events/core.c            | 4 ++--
>  6 files changed, 15 insertions(+), 7 deletions(-)

Looks like you need to update AMD LBR code in amd_pmu_v2_handle_irq().

Thanks,
Namhyung

> 
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 13919eb96931..1ad1efdb33f9 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -2297,6 +2297,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
>  			cpuhw = this_cpu_ptr(&cpu_hw_events);
>  			power_pmu_bhrb_read(event, cpuhw);
>  			data.br_stack = &cpuhw->bhrb_stack;
> +			data.sample_flags |= PERF_SAMPLE_BRANCH_STACK;
>  		}
>  
>  		if (event->attr.sample_type & PERF_SAMPLE_DATA_SRC &&
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index f969410d0c90..bb34a28fa71b 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1714,8 +1714,10 @@ int x86_pmu_handle_irq(struct pt_regs *regs)
>  
>  		perf_sample_data_init(&data, 0, event->hw.last_period);
>  
> -		if (has_branch_stack(event))
> +		if (has_branch_stack(event)) {
>  			data.br_stack = &cpuc->lbr_stack;
> +			data.sample_flags |= PERF_SAMPLE_BRANCH_STACK;
> +		}
>  
>  		if (perf_event_overflow(event, &data, regs))
>  			x86_pmu_stop(event, 0);
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 4fce2bdbbf87..36f95894dd1c 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3004,8 +3004,10 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>  
>  		perf_sample_data_init(&data, 0, event->hw.last_period);
>  
> -		if (has_branch_stack(event))
> +		if (has_branch_stack(event)) {
>  			data.br_stack = &cpuc->lbr_stack;
> +			data.sample_flags |= PERF_SAMPLE_BRANCH_STACK;
> +		}
>  
>  		if (perf_event_overflow(event, &data, regs))
>  			x86_pmu_stop(event, 0);
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index 3af24c4891fb..d5f3007af59d 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1645,8 +1645,10 @@ static void setup_pebs_fixed_sample_data(struct perf_event *event,
>  		data->sample_flags |= PERF_SAMPLE_TIME;
>  	}
>  
> -	if (has_branch_stack(event))
> +	if (has_branch_stack(event)) {
>  		data->br_stack = &cpuc->lbr_stack;
> +		data->sample_flags |= PERF_SAMPLE_BRANCH_STACK;
> +	}
>  }
>  
>  static void adaptive_pebs_save_regs(struct pt_regs *regs,
> @@ -1796,6 +1798,7 @@ static void setup_pebs_adaptive_sample_data(struct perf_event *event,
>  		if (has_branch_stack(event)) {
>  			intel_pmu_store_pebs_lbrs(lbr);
>  			data->br_stack = &cpuc->lbr_stack;
> +			data->sample_flags |= PERF_SAMPLE_BRANCH_STACK;
>  		}
>  	}
>  
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index b0ebbb1377b9..2aec1765b3d5 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1010,7 +1010,6 @@ struct perf_sample_data {
>  	u64				sample_flags;
>  	u64				addr;
>  	struct perf_raw_record		*raw;
> -	struct perf_branch_stack	*br_stack;
>  	u64				period;
>  	union perf_sample_weight	weight;
>  	u64				txn;
> @@ -1020,6 +1019,8 @@ struct perf_sample_data {
>  	 * The other fields, optionally {set,used} by
>  	 * perf_{prepare,output}_sample().
>  	 */
> +	struct perf_branch_stack	*br_stack;
> +
>  	u64				type;
>  	u64				ip;
>  	struct {
> @@ -1060,7 +1061,6 @@ static inline void perf_sample_data_init(struct perf_sample_data *data,
>  	data->sample_flags = 0;
>  	data->addr = addr;
>  	data->raw  = NULL;
> -	data->br_stack = NULL;
>  	data->period = period;
>  	data->weight.full = 0;
>  	data->data_src.val = PERF_MEM_NA;
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index c9b9cb79231a..104c0c9f4e6f 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7052,7 +7052,7 @@ void perf_output_sample(struct perf_output_handle *handle,
>  	}
>  
>  	if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
> -		if (data->br_stack) {
> +		if (data->sample_flags & PERF_SAMPLE_BRANCH_STACK) {
>  			size_t size;
>  
>  			size = data->br_stack->nr
> @@ -7358,7 +7358,7 @@ void perf_prepare_sample(struct perf_event_header *header,
>  
>  	if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
>  		int size = sizeof(u64); /* nr */
> -		if (data->br_stack) {
> +		if (data->sample_flags & PERF_SAMPLE_BRANCH_STACK) {
>  			if (perf_sample_save_hw_index(event))
>  				size += sizeof(u64);
>  
> -- 
> 2.35.1
> 
>