Re: [PATCH v1 3/3] perf parse-events: Add 'X' modifier to exclude an event from being regrouped

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 8/26/2025 5:12 AM, Ian Rogers wrote:
> The function parse_events__sort_events_and_fix_groups is needed to fix
> uncore events like:
> ```
> $ perf stat -e '{data_read,data_write}' ...
> ```
> so that the multiple uncore PMUs have a group each of data_read and
> data_write events.
>
> The same function will perform architecture sorting and group fixing,
> in particular for Intel topdown/perf-metric events. Grouping multiple
> perf metric events together causes perf_event_open to fail as the
> group can only support one. This means command lines like:
> ```
> $ perf stat -e 'slots,slots' ...
> ```
> fail as the slots events are forced into a group together to try to
> satisfy the perf-metric event constraints.
>
> As the user may know better than
> parse_events__sort_events_and_fix_groups add a 'X' modifier to skip
> its regrouping behavior. This allows the following to succeed rather
> than fail on the second slots event being opened:
> ```
> $ perf stat -e 'slots,slots:X' -a sleep 1
>
>  Performance counter stats for 'system wide':
>
>      6,834,154,071      cpu_core/slots/                                                         (50.13%)
>      5,548,629,453      cpu_core/slots/X                                                        (49.87%)
>
>        1.002634606 seconds time elapsed
> ```
>
> Reported-by: Xudong Hao <xudong.hao@intel.com>
> Reported-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> Closes: https://lore.kernel.org/lkml/20250822082233.1850417-1-dapeng1.mi@linux.intel.com/
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/Documentation/perf-list.txt | 1 +
>  tools/perf/util/evsel.h                | 1 +
>  tools/perf/util/parse-events.c         | 5 +++--
>  tools/perf/util/parse-events.h         | 1 +
>  tools/perf/util/parse-events.l         | 5 +++--
>  5 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/Documentation/perf-list.txt b/tools/perf/Documentation/perf-list.txt
> index 28215306a78a..a5039d1614f9 100644
> --- a/tools/perf/Documentation/perf-list.txt
> +++ b/tools/perf/Documentation/perf-list.txt
> @@ -73,6 +73,7 @@ counted. The following modifiers exist:
>   e - group or event are exclusive and do not share the PMU
>   b - use BPF aggregration (see perf stat --bpf-counters)
>   R - retire latency value of the event
> + X - don't regroup the event to match PMUs
>  
>  The 'p' modifier can be used for specifying how precise the instruction
>  address should be. The 'p' modifier can be specified multiple times:
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index e927a3a4fe0e..03f9f22e3a0c 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -89,6 +89,7 @@ struct evsel {
>  		bool			use_config_name;
>  		bool			skippable;
>  		bool			retire_lat;
> +		bool			dont_regroup;
>  		int			bpf_fd;
>  		struct bpf_object	*bpf_obj;
>  		struct list_head	config_terms;
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 8282ddf68b98..43de19551c81 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -1892,6 +1892,8 @@ static int parse_events__modifier_list(struct parse_events_state *parse_state,
>  			evsel->bpf_counter = true;
>  		if (mod.retire_lat)
>  			evsel->retire_lat = true;
> +		if (mod.dont_regroup)
> +			evsel->dont_regroup = true;
>  	}
>  	return 0;
>  }
> @@ -2188,13 +2190,12 @@ static int parse_events__sort_events_and_fix_groups(struct list_head *list)
>  		 * Set the group leader respecting the given groupings and that
>  		 * groups can't span PMUs.
>  		 */
> -		if (!cur_leader) {
> +		if (!cur_leader || pos->dont_regroup) {
>  			cur_leader = pos;
>  			cur_leaders_grp = &pos->core;
>  			if (pos_force_grouped)
>  				force_grouped_leader = pos;
>  		}
> -
>  		cur_leader_pmu_name = cur_leader->group_pmu_name;
>  		if (strcmp(cur_leader_pmu_name, pos_pmu_name)) {
>  			/* PMU changed so the group/leader must change. */
> diff --git a/tools/perf/util/parse-events.h b/tools/perf/util/parse-events.h
> index 62dc7202e3ba..a5c5fc39fd6f 100644
> --- a/tools/perf/util/parse-events.h
> +++ b/tools/perf/util/parse-events.h
> @@ -216,6 +216,7 @@ struct parse_events_modifier {
>  	bool guest : 1;		/* 'G' */
>  	bool host : 1;		/* 'H' */
>  	bool retire_lat : 1;	/* 'R' */
> +	bool dont_regroup : 1;	/* 'X' */
>  };
>  
>  int parse_events__modifier_event(struct parse_events_state *parse_state, void *loc,
> diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
> index 2034590eb789..294e943bcdb4 100644
> --- a/tools/perf/util/parse-events.l
> +++ b/tools/perf/util/parse-events.l
> @@ -206,6 +206,7 @@ static int modifiers(struct parse_events_state *parse_state, yyscan_t scanner)
>  		CASE('e', exclusive);
>  		CASE('b', bpf);
>  		CASE('R', retire_lat);
> +		CASE('X', dont_regroup);
>  		default:
>  			return PE_ERROR;
>  		}
> @@ -251,10 +252,10 @@ term_name	{name_start}[a-zA-Z0-9_*?.\[\]!\-:]*
>  quoted_name	[\']{name_start}[a-zA-Z0-9_*?.\[\]!\-:,\.=]*[\']
>  drv_cfg_term	[a-zA-Z0-9_\.]+(=[a-zA-Z0-9_*?\.:]+)?
>  /*
> - * If you add a modifier you need to update check_modifier().
> + * If you add a modifier you need to update modifiers().
>   * Also, the letters in modifier_event must not be in modifier_bp.
>   */
> -modifier_event	[ukhpPGHSDIWebR]{1,16}
> +modifier_event	[ukhpPGHSDIWebRX]{1,17}
>  modifier_bp	[rwx]{1,3}
>  lc_type 	(L1-dcache|l1-d|l1d|L1-data|L1-icache|l1-i|l1i|L1-instruction|LLC|L2|dTLB|d-tlb|Data-TLB|iTLB|i-tlb|Instruction-TLB|branch|branches|bpu|btb|bpc|node)
>  lc_op_result	(load|loads|read|store|stores|write|prefetch|prefetches|speculative-read|speculative-load|refs|Re

Hi Ian,

It looks the "X" modifier only works for the cases without explicit group,
like this.

sudo ./perf record -e cpu/mem-stores/ppu,cpu/slots/uX -- sleep 1
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.019 MB perf.data (7 samples) ]

Once there is an explicit group, the "X" modifier would not work and the
regroup still happens, e.g.,

sudo ./perf record -e '{cpu/mem-stores/ppu,cpu/slots/uX}' -- sleep 1
WARNING: events were regrouped to match PMUs
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.019 MB perf.data (7 samples) ]

I suppose we should enhance the "X" modifier and make it work in 2nd case
as well. How's your idea?

Thanks,

Dapeng Mi

> ference|ops|access|misses|miss)