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 @@ -114,14 +114,24 @@ 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; }