For some kind of analysis a deltatime output is more human friendly and
reduce the cognitive load for further analysis.

The following output demonstrate the new option "deltatime": calculate
the time difference in relation to the previous event.

  $ perf script --deltatime
  test  2525 [001]     0.000000:            sdt_libev:ev_add: (5635e72a5ebd)
  test  2525 [001]     0.000091:  sdt_libev:epoll_wait_enter: (5635e72a76a9)
  test  2525 [001]     1.000051: sdt_libev:epoll_wait_return: (5635e72a772e) arg1=1
  test  2525 [001]     0.000685:            sdt_libev:ev_add: (5635e72a5ebd)
  test  2525 [001]     0.000048:  sdt_libev:epoll_wait_enter: (5635e72a76a9)
  test  2525 [001]     1.000104: sdt_libev:epoll_wait_return: (5635e72a772e) arg1=1
  test  2525 [001]     0.003895:  sdt_libev:epoll_wait_enter: (5635e72a76a9)
  test  2525 [001]     0.996034: sdt_libev:epoll_wait_return: (5635e72a772e) arg1=1
  test  2525 [001]     0.000058:  sdt_libev:epoll_wait_enter: (5635e72a76a9)
  test  2525 [001]     1.000004: sdt_libev:epoll_wait_return: (5635e72a772e) arg1=1
  test  2525 [001]     0.000064:  sdt_libev:epoll_wait_enter: (5635e72a76a9)
  test  2525 [001]     0.999934: sdt_libev:epoll_wait_return: (5635e72a772e) arg1=1
  test  2525 [001]     0.000056:  sdt_libev:epoll_wait_enter: (5635e72a76a9)
  test  2525 [001]     0.999930: sdt_libev:epoll_wait_return: (5635e72a772e) arg1=1

Committer testing:

So go from default output to --reltime and then this new --deltatime, to
contrast the various timestamp presentation modes for a random perf.data file I
had laying around:

  [root@five ~]# perf script --reltime | head
     perf 442394 [000]     0.000000:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000002:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000004:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000006:  128 cycles: ffffffff972415a1 perf_event_update_userpage+0x1 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000009: 2597 cycles: ffffffff97463785 cap_task_setscheduler+0x5 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000036:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000038:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000040:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000041:  224 cycles: ffffffff9700a53a perf_ibs_handle_irq+0x1da (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000044: 4439 cycles: ffffffff97120d85 put_prev_entity+0x45 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
  [root@five ~]# perf script --deltatime | head
     perf 442394 [000]     0.000000:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000002:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000001:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000001:  128 cycles: ffffffff972415a1 perf_event_update_userpage+0x1 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]     0.000002: 2597 cycles: ffffffff97463785 cap_task_setscheduler+0x5 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000027:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000002:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000001:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000001:  224 cycles: ffffffff9700a53a perf_ibs_handle_irq+0x1da (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]     0.000002: 4439 cycles: ffffffff97120d85 put_prev_entity+0x45 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
  [root@five ~]# perf script | head
     perf 442394 [000]  7600.157861:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]  7600.157864:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]  7600.157866:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]  7600.157867:  128 cycles: ffffffff972415a1 perf_event_update_userpage+0x1 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [000]  7600.157870: 2597 cycles: ffffffff97463785 cap_task_setscheduler+0x5 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]  7600.157897:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]  7600.157900:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]  7600.157901:   16 cycles: ffffffff9706e544 native_write_msr+0x4 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]  7600.157903:  224 cycles: ffffffff9700a53a perf_ibs_handle_irq+0x1da (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
     perf 442394 [001]  7600.157906: 4439 cycles: ffffffff97120d85 put_prev_entity+0x45 (/usr/lib/debug/lib/modules/5.5.10-200.fc31.x86_64/vmlinux)
  [root@five ~]#

Andi suggested we better implement it as a new field, i.e. -F deltatime, like:

  [root@five ~]# perf script -F deltatime
  Invalid field requested.

   Usage: perf script [<options>]
      or: perf script [<options>] record <script> [<record-options>] <command>
      or: perf script [<options>] report <script> [script-args]
      or: perf script [<options>] <script> [<record-options>] <command>
      or: perf script [<options>] <top-script> [script-args]

      -F, --fields <str>    comma separated output fields prepend with 'type:'. +field to add and -field to remove.Valid types: hw,sw,trace,raw,synth. Fields: comm,tid,pid,time,cpu,event,trace,ip,sym,dso,addr,symoff,srcline,period,iregs,uregs,brstack,brstacksym,flags,bpf-output,brstackinsn,brstackoff,callindent,insn,insnlen,synth,phys_addr,metric,misc,ipc
  [root@five ~]#

I.e. we have -F for maximum flexibility:

  [root@five ~]# perf script -F comm,pid,cpu,time | head
            perf 442394 [000]  7600.157861:
            perf 442394 [000]  7600.157864:
            perf 442394 [000]  7600.157866:
            perf 442394 [000]  7600.157867:
            perf 442394 [000]  7600.157870:
            perf 442394 [001]  7600.157897:
            perf 442394 [001]  7600.157900:
            perf 442394 [001]  7600.157901:
            perf 442394 [001]  7600.157903:
            perf 442394 [001]  7600.157906:
  [root@five ~]#

But since we already have --reltime, having --deltatime, documented one after
the other is sensible.
Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20200204173709.489161-1-hagen@jauu.net
[ Added 'perf script' man page entry for --deltatime ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>