[PATCH 2/6] perf record: Fix duplicated sideband events with Intel PT system wide tracing

Adrian Hunter
2020-06-29T19:06:49Z

Commit 0a892c1c9472 ("perf record: Add dummy event during system wide
synthesis") reveals an issue with Intel PT system wide tracing.
Specifically that Intel PT already adds a dummy tracking event, and it is
not the first event. Adding another dummy tracking event causes duplicated
sideband events. Fix by checking for an existing dummy tracking event
first.

Example showing duplicated switch events:

Before:

# perf record -a -e intel_pt//u uname
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.895 MB perf.data ]
# perf script --no-itrace --show-switch-events | head
swapper 0 [007] 6390.516222: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
swapper 0 [007] 6390.516222: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
rcu_sched 11 [007] 6390.516223: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
rcu_sched 11 [007] 6390.516224: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
rcu_sched 11 [007] 6390.516227: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
rcu_sched 11 [007] 6390.516227: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
swapper 0 [007] 6390.516228: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 11/11
swapper 0 [007] 6390.516228: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 11/11
swapper 0 [002] 6390.516415: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 5556/5559
swapper 0 [002] 6390.516416: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 5556/5559

After:

# perf record -a -e intel_pt//u uname
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.868 MB perf.data ]
# perf script --no-itrace --show-switch-events | head
swapper 0 [005] 6450.567013: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 7179/7181
perf 7181 [005] 6450.567014: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
perf 7181 [005] 6450.567028: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
swapper 0 [005] 6450.567029: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 7179/7181
swapper 0 [005] 6450.571699: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
rcu_sched 11 [005] 6450.571700: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
rcu_sched 11 [005] 6450.571702: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
swapper 0 [005] 6450.571703: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 11/11
swapper 0 [005] 6450.579703: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
rcu_sched 11 [005] 6450.579704: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/builtin-record.c | 18 +++++++++---------
tools/perf/util/evlist.c | 12 ++++++++++++
tools/perf/util/evlist.h | 1 +
tools/perf/util/evsel.c | 8 +-------
tools/perf/util/evsel.h | 6 ++++++
5 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index e108d90ae2ed..a37e7910e9e9 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -852,20 +852,20 @@ static int record__open(struct record *rec)
* event synthesis.
*/
if (opts->initial_delay || target__has_cpu(&opts->target)) {
- if (perf_evlist__add_dummy(evlist))
- return -ENOMEM;
+ pos = perf_evlist__get_tracking_event(evlist);
+ if (!evsel__is_dummy_event(pos)) {
+ /* Set up dummy event. */
+ if (perf_evlist__add_dummy(evlist))
+ return -ENOMEM;
+ pos = evlist__last(evlist);
+ perf_evlist__set_tracking_event(evlist, pos);
+ }

- /* Disable tracking of mmaps on lead event. */
- pos = evlist__first(evlist);
- pos->tracking = 0;
- /* Set up dummy event. */
- pos = evlist__last(evlist);
- pos->tracking = 1;
/*
* Enable the dummy event when the process is forked for
* initial_delay, immediately for system wide.
*/
- if (opts->initial_delay)
+ if (opts->initial_delay && !pos->immediate)
pos->core.attr.enable_on_exec = 1;
else
pos->immediate = 1;
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 173b4f0e0e6e..ab48be4cf258 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -1566,6 +1566,18 @@ void perf_evlist__to_front(struct evlist *evlist,
list_splice(&move, &evlist->core.entries);
}

+struct evsel *perf_evlist__get_tracking_event(struct evlist *evlist)
+{
+ struct evsel *evsel;
+
+ evlist__for_each_entry(evlist, evsel) {
+ if (evsel->tracking)
+ return evsel;
+ }
+
+ return evlist__first(evlist);
+}
+
void perf_evlist__set_tracking_event(struct evlist *evlist,
struct evsel *tracking_evsel)
{
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index b6f325dfb4d2..a8081dfc19cf 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -335,6 +335,7 @@ void perf_evlist__to_front(struct evlist *evlist,
evlist__cpu_iter_start(evlist); \
perf_cpu_map__for_each_cpu (cpu, index, (evlist)->core.all_cpus)

+struct evsel *perf_evlist__get_tracking_event(struct evlist *evlist);
void perf_evlist__set_tracking_event(struct evlist *evlist,
struct evsel *tracking_evsel);

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 96e5171dce41..a68ac3632ae6 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -898,12 +898,6 @@ static void evsel__apply_config_terms(struct evsel *evsel,
}
}

-static bool is_dummy_event(struct evsel *evsel)
-{
- return (evsel->core.attr.type == PERF_TYPE_SOFTWARE) &&
- (evsel->core.attr.config == PERF_COUNT_SW_DUMMY);
-}
-
struct evsel_config_term *__evsel__get_config_term(struct evsel *evsel, enum evsel_term_type type)
{
struct evsel_config_term *term, *found_term = NULL;
@@ -1161,7 +1155,7 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
* The software event will trigger -EOPNOTSUPP error out,
* if BRANCH_STACK bit is set.
*/
- if (is_dummy_event(evsel))
+ if (evsel__is_dummy_event(evsel))
evsel__reset_sample_bit(evsel, BRANCH_STACK);
}

diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 0f963c2a88a5..35e3f6d66085 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -399,6 +399,12 @@ static inline bool evsel__has_br_stack(const struct evsel *evsel)
evsel->synth_sample_type & PERF_SAMPLE_BRANCH_STACK;
}

+static inline bool evsel__is_dummy_event(struct evsel *evsel)
+{
+ return (evsel->core.attr.type == PERF_TYPE_SOFTWARE) &&
+ (evsel->core.attr.config == PERF_COUNT_SW_DUMMY);
+}
+
struct perf_env *evsel__env(struct evsel *evsel);

int evsel__store_ids(struct evsel *evsel, struct evlist *evlist);
--
2.17.1