perf db-export: Rename db_export__comm() to db_export__exec_comm()

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>

diff --git a/tools/perf/util/db-export.c b/tools/perf/util/db-export.c
index 34cf197fe74f577db3e3b944a8f1855d56d35c79..8fab57f90cbcbe9579c3577978fcb71903303463 100644 (file)
--- 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 261cfece8deeaada0275e5f81fb4d26c2d28943b..148a657b1887d09b4f5c0bf9d8793862f2390b2a 100644 (file)
--- 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,