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Subject[PATCH 05/28] perf db-export: Rename db_export__comm() to db_export__exec_comm()
Date
From: Adrian Hunter <adrian.hunter@intel.com>

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>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190710085810.1650-3-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.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 34cf197fe74f..8fab57f90cbc 100644
--- a/tools/perf/util/db-export.c
+++ b/tools/perf/util/db-export.c
@@ -105,8 +105,14 @@ 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;

@@ -121,6 +127,16 @@ 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);
}

@@ -313,7 +329,7 @@ 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,
--
2.21.0
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