Re: [PATCH V4 1/7] perf: Add branch stack counters

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

Hi Peter,

Could you please share your comments for this series?

Thanks,
Kan

On 2023-10-04 2:40 p.m., kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.intel.com>
> 
> Currently, the additional information of a branch entry is stored in a
> u64 space. With more and more information added, the space is running
> out. For example, the information of occurrences of events will be added
> for each branch.
> 
> Two places were suggested to append the counters.
> https://lore.kernel.org/lkml/20230802215814.GH231007@hirez.programming.kicks-ass.net/
> One place is right after the flags of each branch entry. It changes the
> existing struct perf_branch_entry. The later ARCH specific
> implementation has to be really careful to consistently pick
> the right struct.
> The other place is right after the entire struct perf_branch_stack.
> The disadvantage is that the pointer of the extra space has to be
> recorded. The common interface perf_sample_save_brstack() has to be
> updated.
> 
> The latter is much straightforward, and should be easily understood and
> maintained. It is implemented in the patch.
> 
> Add a new branch sample type, PERF_SAMPLE_BRANCH_COUNTERS, to indicate
> the event which is recorded in the branch info.
> 
> The "u64 counters" may store the occurrences of several events. The
> information regarding the number of events/counters and the width of
> each counter should be exposed via sysfs as a reference for the perf
> tool. Define the branch_counter_nr and branch_counter_width ABI here.
> The support will be implemented later in the Intel-specific patch.
> 
> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> Cc: Sandipan Das <sandipan.das@amd.com>
> Cc: Ravi Bangoria <ravi.bangoria@amd.com>
> Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
> ---
> 
> Changes since V3:
> - Add a new branch sample type, PERF_SAMPLE_BRANCH_COUNTERS
>   Drop the two  branch sample type in V2.
> - Add the branch_counter_nr and branch_counter_width ABI
> 
>  .../testing/sysfs-bus-event_source-devices-caps |  6 ++++++
>  arch/powerpc/perf/core-book3s.c                 |  2 +-
>  arch/x86/events/amd/core.c                      |  2 +-
>  arch/x86/events/core.c                          |  2 +-
>  arch/x86/events/intel/core.c                    |  2 +-
>  arch/x86/events/intel/ds.c                      |  4 ++--
>  include/linux/perf_event.h                      | 17 ++++++++++++++++-
>  include/uapi/linux/perf_event.h                 | 10 ++++++++++
>  kernel/events/core.c                            |  8 ++++++++
>  9 files changed, 46 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps b/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps
> index 8757dcf41c08..451f0c620aa7 100644
> --- a/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps
> +++ b/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps
> @@ -16,3 +16,9 @@ Description:
>  		Example output in powerpc:
>  		grep . /sys/bus/event_source/devices/cpu/caps/*
>  		/sys/bus/event_source/devices/cpu/caps/pmu_name:POWER9
> +
> +		The "branch_counter_nr" in the supported platform exposes the
> +		maximum number of counters which can be shown in the u64 counters
> +		of PERF_SAMPLE_BRANCH_COUNTERS, while the "branch_counter_width"
> +		exposes the width of each counter. Both of them can be used by
> +		the perf tool to parse the logged counters in each branch.
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 8c1f7def596e..3c14596bbfaf 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -2313,7 +2313,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
>  			struct cpu_hw_events *cpuhw;
>  			cpuhw = this_cpu_ptr(&cpu_hw_events);
>  			power_pmu_bhrb_read(event, cpuhw);
> -			perf_sample_save_brstack(&data, event, &cpuhw->bhrb_stack);
> +			perf_sample_save_brstack(&data, event, &cpuhw->bhrb_stack, NULL);
>  		}
>  
>  		if (event->attr.sample_type & PERF_SAMPLE_DATA_SRC &&
> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> index e24976593a29..4ee6390b45c9 100644
> --- a/arch/x86/events/amd/core.c
> +++ b/arch/x86/events/amd/core.c
> @@ -940,7 +940,7 @@ static int amd_pmu_v2_handle_irq(struct pt_regs *regs)
>  			continue;
>  
>  		if (has_branch_stack(event))
> -			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);
> +			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);
>  
>  		if (perf_event_overflow(event, &data, regs))
>  			x86_pmu_stop(event, 0);
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 40ad1425ffa2..40c9af124128 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1702,7 +1702,7 @@ int x86_pmu_handle_irq(struct pt_regs *regs)
>  		perf_sample_data_init(&data, 0, event->hw.last_period);
>  
>  		if (has_branch_stack(event))
> -			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);
> +			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);
>  
>  		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 a08f794a0e79..41a164764a84 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3047,7 +3047,7 @@ 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))
> -			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);
> +			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);
>  
>  		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 bf97ab904d40..cb3f329f8fa4 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1755,7 +1755,7 @@ static void setup_pebs_fixed_sample_data(struct perf_event *event,
>  		setup_pebs_time(event, data, pebs->tsc);
>  
>  	if (has_branch_stack(event))
> -		perf_sample_save_brstack(data, event, &cpuc->lbr_stack);
> +		perf_sample_save_brstack(data, event, &cpuc->lbr_stack, NULL);
>  }
>  
>  static void adaptive_pebs_save_regs(struct pt_regs *regs,
> @@ -1912,7 +1912,7 @@ static void setup_pebs_adaptive_sample_data(struct perf_event *event,
>  
>  		if (has_branch_stack(event)) {
>  			intel_pmu_store_pebs_lbrs(lbr);
> -			perf_sample_save_brstack(data, event, &cpuc->lbr_stack);
> +			perf_sample_save_brstack(data, event, &cpuc->lbr_stack, NULL);
>  		}
>  	}
>  
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index e85cd1c0eaf3..9ad79f8107cb 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1138,6 +1138,10 @@ static inline bool branch_sample_priv(const struct perf_event *event)
>  	return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_PRIV_SAVE;
>  }
>  
> +static inline bool branch_sample_counters(const struct perf_event *event)
> +{
> +	return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_COUNTERS;
> +}
>  
>  struct perf_sample_data {
>  	/*
> @@ -1172,6 +1176,7 @@ struct perf_sample_data {
>  	struct perf_callchain_entry	*callchain;
>  	struct perf_raw_record		*raw;
>  	struct perf_branch_stack	*br_stack;
> +	u64				*br_stack_cntr;
>  	union perf_sample_weight	weight;
>  	union  perf_mem_data_src	data_src;
>  	u64				txn;
> @@ -1249,7 +1254,8 @@ static inline void perf_sample_save_raw_data(struct perf_sample_data *data,
>  
>  static inline void perf_sample_save_brstack(struct perf_sample_data *data,
>  					    struct perf_event *event,
> -					    struct perf_branch_stack *brs)
> +					    struct perf_branch_stack *brs,
> +					    u64 *brs_cntr)
>  {
>  	int size = sizeof(u64); /* nr */
>  
> @@ -1257,7 +1263,16 @@ static inline void perf_sample_save_brstack(struct perf_sample_data *data,
>  		size += sizeof(u64);
>  	size += brs->nr * sizeof(struct perf_branch_entry);
>  
> +	/*
> +	 * The extension space for counters is appended after the
> +	 * struct perf_branch_stack. It is used to store the occurrences
> +	 * of events of each branch.
> +	 */
> +	if (brs_cntr)
> +		size += brs->nr * sizeof(u64);
> +
>  	data->br_stack = brs;
> +	data->br_stack_cntr = brs_cntr;
>  	data->dyn_size += size;
>  	data->sample_flags |= PERF_SAMPLE_BRANCH_STACK;
>  }
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 39c6a250dd1b..4461f380425b 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -204,6 +204,8 @@ enum perf_branch_sample_type_shift {
>  
>  	PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT	= 18, /* save privilege mode */
>  
> +	PERF_SAMPLE_BRANCH_COUNTERS_SHIFT	= 19, /* save occurrences of events on a branch */
> +
>  	PERF_SAMPLE_BRANCH_MAX_SHIFT		/* non-ABI */
>  };
>  
> @@ -235,6 +237,8 @@ enum perf_branch_sample_type {
>  
>  	PERF_SAMPLE_BRANCH_PRIV_SAVE	= 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT,
>  
> +	PERF_SAMPLE_BRANCH_COUNTERS	= 1U << PERF_SAMPLE_BRANCH_COUNTERS_SHIFT,
> +
>  	PERF_SAMPLE_BRANCH_MAX		= 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
>  };
>  
> @@ -982,6 +986,12 @@ enum perf_event_type {
>  	 *	{ u64                   nr;
>  	 *	  { u64	hw_idx; } && PERF_SAMPLE_BRANCH_HW_INDEX
>  	 *        { u64 from, to, flags } lbr[nr];
> +	 *        #
> +	 *        # The format of the counters is decided by the
> +	 *        # "branch_counter_nr" and "branch_counter_width",
> +	 *        # which are defined in the ABI.
> +	 *        #
> +	 *        { u64 counters; } cntr[nr] && PERF_SAMPLE_BRANCH_COUNTERS
>  	 *      } && PERF_SAMPLE_BRANCH_STACK
>  	 *
>  	 * 	{ u64			abi; # enum perf_sample_regs_abi
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 41e28f64a4a9..56b08ffeed2f 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7336,6 +7336,14 @@ void perf_output_sample(struct perf_output_handle *handle,
>  			if (branch_sample_hw_index(event))
>  				perf_output_put(handle, data->br_stack->hw_idx);
>  			perf_output_copy(handle, data->br_stack->entries, size);
> +			/*
> +			 * Add the extension space which is appended
> +			 * right after the struct perf_branch_stack.
> +			 */
> +			if (data->br_stack_cntr) {
> +				size = data->br_stack->nr * sizeof(u64);
> +				perf_output_copy(handle, data->br_stack_cntr, size);
> +			}
>  		} else {
>  			/*
>  			 * we always store at least the value of nr