Commit 1e53e9d1 authored by Dapeng Mi's avatar Dapeng Mi Committed by Namhyung Kim
Browse files

perf x86/topdown: Correct leader selection with sample_read enabled 



Addresses an issue where, in the absence of a topdown metrics event
within a sampling group, the slots event was incorrectly bypassed as
the sampling leader when sample_read was enabled.

perf record -e '{slots,branches}:S' -c 10000 -vv sleep 1

In this case, the slots event should be sampled as leader but the
branches event is sampled in fact like the verbose output shows.

perf_event_attr:
  type                             4 (cpu)
  size                             168
  config                           0x400 (slots)
  sample_type                      IP|TID|TIME|READ|CPU|IDENTIFIER
  read_format                      ID|GROUP|LOST
  disabled                         1
  sample_id_all                    1
  exclude_guest                    1
------------------------------------------------------------
sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8 = 5
------------------------------------------------------------
perf_event_attr:
  type                             0 (PERF_TYPE_HARDWARE)
  size                             168
  config                           0x4 (PERF_COUNT_HW_BRANCH_INSTRUCTIONS)
  { sample_period, sample_freq }   10000
  sample_type                      IP|TID|TIME|READ|CPU|IDENTIFIER
  read_format                      ID|GROUP|LOST
  sample_id_all                    1
  exclude_guest                    1

The sample period of slots event instead of branches event is reset to
0.

This fix ensures the slots event remains the leader under these
conditions.

Reviewed-by: default avatarKan Liang <kan.liang@linux.intel.com>
Signed-off-by: default avatarDapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Yongwei Ma <yongwei.ma@intel.com>
Link: https://lore.kernel.org/r/20240913084712.13861-3-dapeng1.mi@linux.intel.com


Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent 39820ced

tools/perf/arch/x86/util/topdown.c

+16 −2
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include "api/fs/fs.h"

#include "util/evsel.h"

#include "util/evlist.h"

#include "util/pmu.h"

#include "util/pmus.h"

#include "util/topdown.h"
@@ -87,11 +88,24 @@ bool arch_is_topdown_metrics(const struct evsel *evsel) 
 */

bool arch_topdown_sample_read(struct evsel *leader)

{

	struct evsel *evsel;



	if (!evsel__sys_has_perf_metrics(leader))

		return false;



	if (arch_is_topdown_slots(leader))

	if (!arch_is_topdown_slots(leader))

		return false;



	/*

	 * If slots event as leader event but no topdown metric events

	 * in group, slots event should still sample as leader.

	 */

	evlist__for_each_entry(leader->evlist, evsel) {

		if (evsel->core.leader != leader->core.leader)

			return false;

		if (evsel != leader && arch_is_topdown_metrics(evsel))

			return true;

	}



	return false;

}