In the default 'perf record' configuration, all samples are processed,
to create the HEADER_BUILD_ID table. So it's very easy to get the
first/last samples and save the time to perf file header via the
function write_sample_time().

Later, at post processing time, perf report/script will fetch the time
from perf file header.

Committer testing:

  # perf record -a sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 2.099 MB perf.data (1101 samples) ]
  [root@jouet home]# perf report --header | grep "time of "
  # time of first sample : 22947.909226
  # time of last sample : 22948.910704
  #
  # perf report -D | grep PERF_RECORD_SAMPLE\(
  0 22947909226101 0x20bb68 [0x30]: PERF_RECORD_SAMPLE(IP, 0x4001): 0/0: 0xffffffffa21b1af3 period: 1 addr: 0
  0 22947909229928 0x20bb98 [0x30]: PERF_RECORD_SAMPLE(IP, 0x4001): 0/0: 0xffffffffa200d204 period: 1 addr: 0
  <SNIP>
  3 22948910397351 0x219360 [0x30]: PERF_RECORD_SAMPLE(IP, 0x4001): 28251/28251: 0xffffffffa22071d8 period: 169518 addr: 0
  0 22948910652380 0x20f120 [0x30]: PERF_RECORD_SAMPLE(IP, 0x4001): 0/0: 0xffffffffa2856816 period: 198807 addr: 0
  2 22948910704034 0x2172d0 [0x30]: PERF_RECORD_SAMPLE(IP, 0x4001): 0/0: 0xffffffffa2856816 period: 88111 addr: 0
  #

Changelog:

v7: Just update the patch description according to Arnaldo's suggestion.

v6: Currently '--buildid-all' is not enabled at default. So the walking
    on all samples is the default operation. There is no big overhead
    to calculate the timestamp boundary in process_sample_event handler
    once we already go through all samples. So the timestamp boundary
    calculation is enabled by default when '--buildid-all' is not enabled.

    While if '--buildid-all' is enabled, we creates a new option
    "--timestamp-boundary" for user to decide if it enables the
    timestamp boundary calculation.

v5: There is an issue that the sample walking can only work when
    '--buildid-all' is not enabled. So we need to let the walking
    be able to work even if '--buildid-all' is enabled and let the
    processing skips the dso hit marking for this case.

    At first, I want to provide a new option "--record-time-boundaries".
    While after consideration, I think a new option is not very
    necessary.

v3: Remove the definitions of first_sample_time and last_sample_time
    from struct record and directly save them in perf_evlist.
Signed-off-by: NJin Yao <yao.jin@linux.intel.com>
Acked-by: NJiri Olsa <jolsa@kernel.org>
Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1512738826-2628-3-git-send-email-yao.jin@linux.intel.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>