[PATCH 02/21] perf db-export: Rename db_export__comm() to db_export__exec_comm()

Adrian Hunter
2019-07-10T09:00:49Z

Rename db_export__comm() to db_export__exec_comm() to better reflect
what it does and add explanatory comments.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/db-export.c | 22 +++++++++++++++++++---
tools/perf/util/db-export.h | 4 ++--
2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/db-export.c b/tools/perf/util/db-export.c
index f36970018df3..bb696559cd9a 100644
--- a/tools/perf/util/db-export.c
+++ b/tools/perf/util/db-export.c
@@ -104,8 +104,14 @@ int db_export__thread(struct db_export *dbe, struct thread *thread,
return err;
}

-int db_export__comm(struct db_export *dbe, struct comm *comm,
- struct thread *main_thread)
+/*
+ * Export the "exec" comm. The "exec" comm is the program / application command
+ * name at the time it first executes. It is used to group threads for the same
+ * program. Note that the main thread pid (or thread group id tgid) cannot be
+ * used because it does not change when a new program is exec'ed.
+ */
+int db_export__exec_comm(struct db_export *dbe, struct comm *comm,
+ struct thread *main_thread)
{
int err;

@@ -120,6 +126,16 @@ int db_export__comm(struct db_export *dbe, struct comm *comm,
return err;
}

+ /*
+ * Record the main thread for this comm. Note that the main thread can
+ * have many "exec" comms because there will be a new one every time it
+ * exec's. An "exec" comm however will only ever have 1 main thread.
+ * That is different to any other threads for that same program because
+ * exec() will effectively kill them, so the relationship between the
+ * "exec" comm and non-main threads is 1-to-1. That is why
+ * db_export__comm_thread() is called here for the main thread, but it
+ * is called for non-main threads when they are exported.
+ */
return db_export__comm_thread(dbe, comm, main_thread);
}

@@ -312,7 +328,7 @@ int db_export__sample(struct db_export *dbe, union perf_event *event,
goto out_put;

if (comm) {
- err = db_export__comm(dbe, comm, main_thread);
+ err = db_export__exec_comm(dbe, comm, main_thread);
if (err)
goto out_put;
es.comm_db_id = comm->db_id;
diff --git a/tools/perf/util/db-export.h b/tools/perf/util/db-export.h
index 261cfece8dee..148a657b1887 100644
--- a/tools/perf/util/db-export.h
+++ b/tools/perf/util/db-export.h
@@ -76,8 +76,8 @@ int db_export__evsel(struct db_export *dbe, struct perf_evsel *evsel);
int db_export__machine(struct db_export *dbe, struct machine *machine);
int db_export__thread(struct db_export *dbe, struct thread *thread,
struct machine *machine, struct comm *comm);
-int db_export__comm(struct db_export *dbe, struct comm *comm,
- struct thread *main_thread);
+int db_export__exec_comm(struct db_export *dbe, struct comm *comm,
+ struct thread *main_thread);
int db_export__comm_thread(struct db_export *dbe, struct comm *comm,
struct thread *thread);
int db_export__dso(struct db_export *dbe, struct dso *dso,
--
2.17.1