It's now possible to specify the threshold time for perf.data like:

  $ perf record --switch-output=30s ...

Once it's reached, the current data are dumped in to the
perf.data.<timestamp> file and session does on.

  $ perf record --switch-output=30s ...
  [ perf record: dump data: Woken up 44 times ]
  [ perf record: Dump perf.data.2017010213043746 ]
  ...

The time is expected to be a number with appended unit
character - s/m/h/d.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Wang Nan <wangnan0@huawei.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1483955520-29063-7-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>