It is useful for debug to see file descriptors for each event.

Before:

  $ perf stat -vvv -e cycles,cache-misses ls
  ...
  sys_perf_event_open: pid 12146  cpu -1  group_fd -1  flags 0x8
  ...
  sys_perf_event_open: pid 12146  cpu -1  group_fd 3  flags 0x8
  sys_perf_event_open failed, error -13

Now:

  $ perf stat -vvv -e cycles,cache-misses ls
  ...
  sys_perf_event_open: pid 12858  cpu -1  group_fd -1  flags 0x8 = 3
  ...
  sys_perf_event_open: pid 12858  cpu -1  group_fd 3  flags 0x8
  sys_perf_event_open failed, error -13
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Joe Mario <jmario@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1479764011-10732-2-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>