The perf ftrace latency is to get a histogram of function execution
time.  Users should give a function name using -T option.

This is implemented using function_graph tracer with the given
function only.  And it parses the output to extract the time.

  $ sudo perf ftrace latency -a -T mutex_lock sleep 1
  #   DURATION     |      COUNT | GRAPH                          |
       0 - 1    us |       4596 | ########################       |
       1 - 2    us |       1680 | #########                      |
       2 - 4    us |       1106 | #####                          |
       4 - 8    us |        546 | ##                             |
       8 - 16   us |        562 | ###                            |
      16 - 32   us |          1 |                                |
      32 - 64   us |          0 |                                |
      64 - 128  us |          0 |                                |
     128 - 256  us |          0 |                                |
     256 - 512  us |          0 |                                |
     512 - 1024 us |          0 |                                |
       1 - 2    ms |          0 |                                |
       2 - 4    ms |          0 |                                |
       4 - 8    ms |          0 |                                |
       8 - 16   ms |          0 |                                |
      16 - 32   ms |          0 |                                |
      32 - 64   ms |          0 |                                |
      64 - 128  ms |          0 |                                |
     128 - 256  ms |          0 |                                |
     256 - 512  ms |          0 |                                |
     512 - 1024 ms |          0 |                                |
       1 - ...   s |          0 |                                |

Committer testing:

Latency for the __handle_mm_fault kernel function, system wide for 1
second, see how one can go from the usual 'perf ftrace' output, now the
same as for the 'perf ftrace trace' subcommand, to the new 'perf ftrace
latency' subcommand:

  # perf ftrace -T __handle_mm_fault -a sleep 1 | wc -l
  709
  # perf ftrace -T __handle_mm_fault -a sleep 1 | wc -l
  510
  # perf ftrace -T __handle_mm_fault -a sleep 1 | head -20
  # tracer: function
  #
  # entries-in-buffer/entries-written: 0/0   #P:32
  #
  #           TASK-PID     CPU#     TIMESTAMP  FUNCTION
  #              | |         |         |         |
         perf-exec-1685104 [007]  90638.894613: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894620: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894622: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894635: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894688: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894702: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894714: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894728: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894740: __handle_mm_fault <-handle_mm_fault
         perf-exec-1685104 [007]  90638.894751: __handle_mm_fault <-handle_mm_fault
             sleep-1685104 [007]  90638.894962: __handle_mm_fault <-handle_mm_fault
             sleep-1685104 [007]  90638.894977: __handle_mm_fault <-handle_mm_fault
             sleep-1685104 [007]  90638.894983: __handle_mm_fault <-handle_mm_fault
             sleep-1685104 [007]  90638.894995: __handle_mm_fault <-handle_mm_fault
  # perf ftrace latency -T __handle_mm_fault -a sleep 1
  #   DURATION     |      COUNT | GRAPH                                          |
       0 - 1    us |        125 | ######                                         |
       1 - 2    us |        249 | #############                                  |
       2 - 4    us |        455 | ########################                       |
       4 - 8    us |         37 | #                                              |
       8 - 16   us |          0 |                                                |
      16 - 32   us |          0 |                                                |
      32 - 64   us |          0 |                                                |
      64 - 128  us |          0 |                                                |
     128 - 256  us |          0 |                                                |
     256 - 512  us |          0 |                                                |
     512 - 1024 us |          0 |                                                |
       1 - 2    ms |          0 |                                                |
       2 - 4    ms |          0 |                                                |
       4 - 8    ms |          0 |                                                |
       8 - 16   ms |          0 |                                                |
      16 - 32   ms |          0 |                                                |
      32 - 64   ms |          0 |                                                |
      64 - 128  ms |          0 |                                                |
     128 - 256  ms |          0 |                                                |
     256 - 512  ms |          0 |                                                |
     512 - 1024 ms |          0 |                                                |
       1 - ...   s |          0 |                                                |
  #
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Changbin Du <changbin.du@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20211215185154.360314-4-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>