perf pmus: Describe semantics of 'core_pmus' and 'other_pmus'

Notion of 'core_pmus' and 'other_pmus' are independent of hw core and
uncore pmus. For example, AMD IBS PMUs are present in each SMT-thread
but they belongs to 'other_pmus'. Add a comment describing what these
list contains and how they are treated.

Reviewed-by: Ian Rogers <[email protected]>
Signed-off-by: Ravi Bangoria <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Ali Saidi <[email protected]>
Cc: Ananth Narayan <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sandipan Das <[email protected]>
Cc: Santosh Shukla <[email protected]>
Cc: Thomas Richter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
index e1d0a93147e5..8c50ab8894b7 100644
--- a/tools/perf/util/pmus.c
+++ b/tools/perf/util/pmus.c
@@ -12,6 +12,21 @@
 #include "pmu.h"
 #include "print-events.h"
 
+/*
+ * core_pmus:  A PMU belongs to core_pmus if it's name is "cpu" or it's sysfs
+ *             directory contains "cpus" file. All PMUs belonging to core_pmus
+ *             must have pmu->is_core=1. If there are more than one PMU in
+ *             this list, perf interprets it as a heterogeneous platform.
+ *             (FWIW, certain ARM platforms having heterogeneous cores uses
+ *             homogeneous PMU, and thus they are treated as homogeneous
+ *             platform by perf because core_pmus will have only one entry)
+ * other_pmus: All other PMUs which are not part of core_pmus list. It doesn't
+ *             matter whether PMU is present per SMT-thread or outside of the
+ *             core in the hw. For e.g., an instance of AMD ibs_fetch// and
+ *             ibs_op// PMUs is present in each hw SMT thread, however they
+ *             are captured under other_pmus. PMUs belonging to other_pmus
+ *             must have pmu->is_core=0 but pmu->is_uncore could be 0 or 1.
+ */
 static LIST_HEAD(core_pmus);
 static LIST_HEAD(other_pmus);
 static bool read_sysfs_core_pmus;