perf report: Report OOM in status line in the GTK UI [Linux 5.1]

perf report: Report OOM in status line in the GTK UI [Linux 5.1]

This Linux kernel change "perf report: Report OOM in status line in the GTK UI" is included in the Linux 5.1 release. This change is authored by Thomas Richter <tmricht [at] linux.ibm.com> on Tue Apr 23 12:53:03 2019 +0200. The commit for this change in Linux stable tree is 167e418 (patch).

perf report: Report OOM in status line in the GTK UI

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
called:

  perf_session__process_event()
  + 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 ‘perf_session__process_events’:
  util/session.c:1936:7: error: ‘skip’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
     err = skip;
     ~~~~^~~~~~
  util/session.c:1874:6: note: ‘skip’ was declared here
    s64 skip;
        ^~~~
  cc1: all warnings being treated as errors

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20190423105303.61683-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

There are 8 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 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 b17f1c9..bad5f87 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1928,12 +1928,14 @@ struct reader {

    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;
    }

Leave a Reply

Your email address will not be published. Required fields are marked *