[PATCH 4.4 06/78] perf db-export: Fix thread__exec_comm()

Greg Kroah-Hartman
2019-08-22T17:22:37Z

From: Adrian Hunter <adrian.hunter@intel.com>

commit 3de7ae0b2a1d86dbb23d0cb135150534fdb2e836 upstream.

Threads synthesized from /proc have comms with a start time of zero, and
not marked as "exec". Currently, there can be 2 such comms. The first is
created by processing a synthesized fork event and is set to the
parent's comm string, and the second by processing a synthesized comm
event set to the thread's current comm string.

In the absence of an "exec" comm, thread__exec_comm() picks the last
(oldest) comm, which, in the case above, is the parent's comm string.
For a main thread, that is very probably wrong. Use the second-to-last
in that case.

This affects only db-export because it is the only user of
thread__exec_comm().

Example:

$ sudo perf record -a -o pt-a-sleep-1 -e intel_pt//u -- sleep 1
$ sudo chown ahunter pt-a-sleep-1

Before:

$ perf script -i pt-a-sleep-1 --itrace=bep -s tools/perf/scripts/python/export-to-sqlite.py pt-a-sleep-1.db branches calls
$ sqlite3 -header -column pt-a-sleep-1.db 'select * from comm_threads_view'
comm_id command thread_id pid tid
---------- ---------- ---------- ---------- ----------
1 swapper 1 0 0
2 rcu_sched 2 10 10
3 kthreadd 3 78 78
5 sudo 4 15180 15180
5 sudo 5 15180 15182
7 kworker/4: 6 10335 10335
8 kthreadd 7 55 55
10 systemd 8 865 865
10 systemd 9 865 875
13 perf 10 15181 15181
15 sleep 10 15181 15181
16 kworker/3: 11 14179 14179
17 kthreadd 12 29376 29376
19 systemd 13 746 746
21 systemd 14 401 401
23 systemd 15 879 879
23 systemd 16 879 945
25 kthreadd 17 556 556
27 kworker/u1 18 14136 14136
28 kworker/u1 19 15021 15021
29 kthreadd 20 509 509
31 systemd 21 836 836
31 systemd 22 836 967
33 systemd 23 1148 1148
33 systemd 24 1148 1163
35 kworker/2: 25 17988 17988
36 kworker/0: 26 13478 13478

After:

$ perf script -i pt-a-sleep-1 --itrace=bep -s tools/perf/scripts/python/export-to-sqlite.py pt-a-sleep-1b.db branches calls
$ sqlite3 -header -column pt-a-sleep-1b.db 'select * from comm_threads_view'
comm_id command thread_id pid tid
---------- ---------- ---------- ---------- ----------
1 swapper 1 0 0
2 rcu_sched 2 10 10
3 kswapd0 3 78 78
4 perf 4 15180 15180
4 perf 5 15180 15182
6 kworker/4: 6 10335 10335
7 kcompactd0 7 55 55
8 accounts-d 8 865 865
8 accounts-d 9 865 875
10 perf 10 15181 15181
12 sleep 10 15181 15181
13 kworker/3: 11 14179 14179
14 kworker/1: 12 29376 29376
15 haveged 13 746 746
16 systemd-jo 14 401 401
17 NetworkMan 15 879 879
17 NetworkMan 16 879 945
19 irq/131-iw 17 556 556
20 kworker/u1 18 14136 14136
21 kworker/u1 19 15021 15021
22 kworker/u1 20 509 509
23 thermald 21 836 836
23 thermald 22 836 967
25 unity-sett 23 1148 1148
25 unity-sett 24 1148 1163
27 kworker/2: 25 17988 17988
28 kworker/0: 26 13478 13478

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 65de51f93ebf ("perf tools: Identify which comms are from exec")
Link: http://lkml.kernel.org/r/20190808064823.14846-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
tools/perf/util/thread.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -110,14 +110,24 @@ struct comm *thread__comm(const struct t

struct comm *thread__exec_comm(const struct thread *thread)
{
- struct comm *comm, *last = NULL;
+ struct comm *comm, *last = NULL, *second_last = NULL;

list_for_each_entry(comm, &thread->comm_list, list) {
if (comm->exec)
return comm;
+ second_last = last;
last = comm;
}

+ /*
+ * 'last' with no start time might be the parent's comm of a synthesized
+ * thread (created by processing a synthesized fork event). For a main
+ * thread, that is very probably wrong. Prefer a later comm to avoid
+ * that case.
+ */
+ if (second_last && !last->start && thread->pid_ == thread->tid)
+ return second_last;
+
return last;
}