After pmu_add_cpu_aliases() is called, perf_pmu__num_events() returns an
incorrect value that double counts common events and doesn't match the
actual count of events in the alias list. This is because after
'cpu_aliases_added == true', the number of events returned is
'sysfs_aliases + cpu_json_aliases'. But when adding 'case
EVENT_SRC_SYSFS' events, 'sysfs_aliases' and 'cpu_json_aliases' are both
incremented together, failing to account that these ones overlap and
only add a single item to the list. Fix it by adding another counter for
overlapping events which doesn't influence 'cpu_json_aliases'.

There doesn't seem to be a current issue because it's used in perf list
before pmu_add_cpu_aliases() so the correct value is returned. Other
uses in tests may also miss it for other reasons like only looking at
uncore events. However it's marked as a fixes commit in case any new fix
with new uses of perf_pmu__num_events() is backported.

Fixes: d9c5f5f94c2d ("perf pmu: Count sys and cpuid JSON events separately")
Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/perf/util/pmu.c | 7 ++++---
 tools/perf/util/pmu.h | 5 +++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index ec3878c890a9..72aa6167c090 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -596,7 +596,7 @@ static int perf_pmu__new_alias(struct perf_pmu *pmu, const char *name,
 			};
 			if (pmu_events_table__find_event(pmu->events_table, pmu, name,
 							 update_alias, &data) == 0)
-				pmu->cpu_json_aliases++;
+				pmu->cpu_common_json_aliases++;
 		}
 		pmu->sysfs_aliases++;
 		break;
@@ -1884,9 +1884,10 @@ size_t perf_pmu__num_events(struct perf_pmu *pmu)
 	if (pmu->cpu_aliases_added)
 		 nr += pmu->cpu_json_aliases;
 	else if (pmu->events_table)
-		nr += pmu_events_table__num_events(pmu->events_table, pmu) - pmu->cpu_json_aliases;
+		nr += pmu_events_table__num_events(pmu->events_table, pmu) -
+			pmu->cpu_common_json_aliases;
 	else
-		assert(pmu->cpu_json_aliases == 0);
+		assert(pmu->cpu_json_aliases == 0 && pmu->cpu_common_json_aliases == 0);
 
 	if (perf_pmu__is_tool(pmu))
 		nr -= tool_pmu__num_skip_events();
diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
index f5306428c03f..b93014cc3670 100644
--- a/tools/perf/util/pmu.h
+++ b/tools/perf/util/pmu.h
@@ -136,6 +136,11 @@ struct perf_pmu {
 	uint32_t cpu_json_aliases;
 	/** @sys_json_aliases: Number of json event aliases loaded matching the PMU's identifier. */
 	uint32_t sys_json_aliases;
+	/**
+	 * @cpu_common_json_aliases: Number of json events that overlapped with sysfs when
+	 * loading all sysfs events.
+	 */
+	uint32_t cpu_common_json_aliases;
 	/** @sysfs_aliases_loaded: Are sysfs aliases loaded from disk? */
 	bool sysfs_aliases_loaded;
 	/**
-- 
2.34.1

On Tue, Feb 25, 2025 at 8:47 AM James Clark <james.clark@linaro.org> wrote:
>
> After pmu_add_cpu_aliases() is called, perf_pmu__num_events() returns an
> incorrect value that double counts common events and doesn't match the
> actual count of events in the alias list. This is because after
> 'cpu_aliases_added == true', the number of events returned is
> 'sysfs_aliases + cpu_json_aliases'. But when adding 'case
> EVENT_SRC_SYSFS' events, 'sysfs_aliases' and 'cpu_json_aliases' are both
> incremented together, failing to account that these ones overlap and
> only add a single item to the list. Fix it by adding another counter for
> overlapping events which doesn't influence 'cpu_json_aliases'.
>
> There doesn't seem to be a current issue because it's used in perf list
> before pmu_add_cpu_aliases() so the correct value is returned. Other
> uses in tests may also miss it for other reasons like only looking at
> uncore events. However it's marked as a fixes commit in case any new fix
> with new uses of perf_pmu__num_events() is backported.
>
> Fixes: d9c5f5f94c2d ("perf pmu: Count sys and cpuid JSON events separately")
> Signed-off-by: James Clark <james.clark@linaro.org>

Reviewed-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> ---
>  tools/perf/util/pmu.c | 7 ++++---
>  tools/perf/util/pmu.h | 5 +++++
>  2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index ec3878c890a9..72aa6167c090 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -596,7 +596,7 @@ static int perf_pmu__new_alias(struct perf_pmu *pmu, const char *name,
>                         };
>                         if (pmu_events_table__find_event(pmu->events_table, pmu, name,
>                                                          update_alias, &data) == 0)
> -                               pmu->cpu_json_aliases++;
> +                               pmu->cpu_common_json_aliases++;
>                 }
>                 pmu->sysfs_aliases++;
>                 break;
> @@ -1884,9 +1884,10 @@ size_t perf_pmu__num_events(struct perf_pmu *pmu)
>         if (pmu->cpu_aliases_added)
>                  nr += pmu->cpu_json_aliases;
>         else if (pmu->events_table)
> -               nr += pmu_events_table__num_events(pmu->events_table, pmu) - pmu->cpu_json_aliases;
> +               nr += pmu_events_table__num_events(pmu->events_table, pmu) -
> +                       pmu->cpu_common_json_aliases;
>         else
> -               assert(pmu->cpu_json_aliases == 0);
> +               assert(pmu->cpu_json_aliases == 0 && pmu->cpu_common_json_aliases == 0);
>
>         if (perf_pmu__is_tool(pmu))
>                 nr -= tool_pmu__num_skip_events();
> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
> index f5306428c03f..b93014cc3670 100644
> --- a/tools/perf/util/pmu.h
> +++ b/tools/perf/util/pmu.h
> @@ -136,6 +136,11 @@ struct perf_pmu {
>         uint32_t cpu_json_aliases;
>         /** @sys_json_aliases: Number of json event aliases loaded matching the PMU's identifier. */
>         uint32_t sys_json_aliases;
> +       /**
> +        * @cpu_common_json_aliases: Number of json events that overlapped with sysfs when
> +        * loading all sysfs events.
> +        */
> +       uint32_t cpu_common_json_aliases;
>         /** @sysfs_aliases_loaded: Are sysfs aliases loaded from disk? */
>         bool sysfs_aliases_loaded;
>         /**
> --
> 2.34.1
>