[PATCH 06/11] perf report: Report OOM in status line in the GTK UI

From: Arnaldo Carvalho de Melo
Date: Thu May 02 2019 - 20:26:33 EST

From: Thomas Richter <tmricht@xxxxxxxxxxxxx>

An -ENOMEM error is not reported in the GTK GUI. Instead this error
message pops up on the screen:

[root@m35lp76 perf]# ./perf report -i perf.data.error68-1

Processing events... [974K/3M]
Error:failed to process sample

0xf4198 [0x8]: failed to process type: 68

However when I use the same perf.data file with --stdio it works:

[root@m35lp76 perf]# ./perf report -i perf.data.error68-1 --stdio \
| head -12

# Total Lost Samples: 0
# Samples: 76K of event 'cycles'
# Event count (approx.): 99056160000
# Overhead Command Shared Object Symbol
# ........ ............... ................. .........
8.81% find [kernel.kallsyms] [k] ftrace_likely_update
8.74% swapper [kernel.kallsyms] [k] ftrace_likely_update
8.34% sshd [kernel.kallsyms] [k] ftrace_likely_update
2.19% kworker/u512:1- [kernel.kallsyms] [k] ftrace_likely_update

The sample precentage is a bit low.....

The GUI always fails in the FINISHED_ROUND event (68) and does not
indicate the reason why.

When happened is the following. Perf report calls a lot of functions and
down deep when a FINISHED_ROUND event is processed, these functions are

+ perf_session__process_user_event()
+ process_finished_round()
+ ordered_events__flush()
+ __ordered_events__flush()
+ do_flush()
+ ordered_events__deliver_event()
+ perf_session__deliver_event()
+ machine__deliver_event()
+ perf_evlist__deliver_event()
+ process_sample_event()
+ hist_entry_iter_add() --> only called in GUI case!!!
+ hist_iter__report__callback()
+ symbol__inc_addr_sample()

Now this functions runs out of memory and
returns -ENOMEM. This is reported all the way up
until function

perf_session__process_event() returns to its caller, where -ENOMEM is
changed to -EINVAL and processing stops:

if ((skip = perf_session__process_event(session, event, head)) < 0) {
pr_err("%#" PRIx64 " [%#x]: failed to process type: %d\n",
head, event->header.size, event->header.type);
err = -EINVAL;
goto out_err;

This occurred in the FINISHED_ROUND event when it has to process some
10000 entries and ran out of memory.

This patch indicates the root cause and displays it in the status line
of ther perf report GUI.

Output before (on GUI status line):

0xf4198 [0x8]: failed to process type: 68

Output after:

0xf4198 [0x8]: failed to process type: 68 [not enough memory]

Committer notes:

the 'skip' variable needs to be initialized to -EINVAL, so that when the
size is less than sizeof(struct perf_event_attr) we avoid this valid
compiler warning:

util/session.c: In function âperf_session__process_eventsâ:
util/session.c:1936:7: error: âskipâ may be used uninitialized in this function [-Werror=maybe-uninitialized]
err = skip;
util/session.c:1874:6: note: âskipâ was declared here
s64 skip;
cc1: all warnings being treated as errors

Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
Reviewed-by: Hendrik Brueckner <brueckner@xxxxxxxxxxxxx>
Reviewed-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20190423105303.61683-1-tmricht@xxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
tools/perf/util/session.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index b17f1c9bc965..bad5f87ae001 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1928,12 +1928,14 @@ reader__process_events(struct reader *rd, struct perf_session *session,

size = event->header.size;

+ skip = -EINVAL;
if (size < sizeof(struct perf_event_header) ||
(skip = rd->process(session, event, file_pos)) < 0) {
- pr_err("%#" PRIx64 " [%#x]: failed to process type: %d\n",
+ pr_err("%#" PRIx64 " [%#x]: failed to process type: %d [%s]\n",
file_offset + head, event->header.size,
- event->header.type);
- err = -EINVAL;
+ event->header.type, strerror(-skip));
+ err = skip;
goto out;