perf ftrace: Check min/max latency only with bucket range

It's an optional feature and remains 0 when bucket range is not given.
And it makes the histogram goes to the last entry always because any
latency (num) is greater than or equal to 0.

Before:

  $ sudo ./perf ftrace latency -a -T do_futex sleep 1
  #   DURATION     |      COUNT | GRAPH                                          |
       0 -    0 us |          0 |                                                |
       1 -    2 us |          0 |                                                |
       2 -    4 us |          0 |                                                |
       4 -    8 us |          0 |                                                |
       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  |       1353 | ############################################## |

After:

  $ sudo ./perf ftrace latency -a -T do_futex sleep 1
  #   DURATION     |      COUNT | GRAPH                                          |
       0 -    0 us |        321 | ###########                                    |
       1 -    2 us |        132 | ####                                           |
       2 -    4 us |        202 | #######                                        |
       4 -    8 us |        188 | ######                                         |
       8 -   16 us |         16 |                                                |
      16 -   32 us |         12 |                                                |
      32 -   64 us |         30 | #                                              |
      64 -  128 us |         98 | ###                                            |
     128 -  256 us |         53 | #                                              |
     256 -  512 us |         57 | ##                                             |
     512 - 1024 us |          9 |                                                |
       1 -    2 ms |          9 |                                                |
       2 -    4 ms |          1 |                                                |
       4 -    8 ms |         98 | ###                                            |
       8 -   16 ms |          5 |                                                |
      16 -   32 ms |          7 |                                                |
      32 -   64 ms |         32 | #                                              |
      64 -  128 ms |         10 |                                                |
     128 -  256 ms |         10 |                                                |
     256 -  512 ms |          2 |                                                |
     512 - 1024 ms |          0 |                                                |
       1 - ...  s  |          0 |                                                |

Fixes: 690a052 ("perf ftrace latency: Add --max-latency option")
Reviewed-by: Gabriele Monaco <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Tested-by: Gabriele Monaco <[email protected]
Cc: Adrian Hunter <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: namhyung

tools/perf/builtin-ftrace.c

@@ -796,8 +796,10 @@ static void make_histogram(struct perf_ftrace *ftrace, int buckets[],
 			// than the min latency desired.
 			if (num > 0) // 1st entry: [ 1 unit .. bucket_range units ]
 				i = num / ftrace->bucket_range + 1;
+			if (num >= max_latency - min_latency)
+				i = NUM_BUCKET -1;
 		}
-		if (i >= NUM_BUCKET || num >= max_latency - min_latency)
+		if (i >= NUM_BUCKET)
 			i = NUM_BUCKET - 1;
 
 		num += min_latency;
@@ -1738,7 +1740,7 @@ int cmd_ftrace(int argc, const char **argv)
 			ret = -EINVAL;
 			goto out_delete_filters;
 		}
-		if (!ftrace.min_latency) {
+		if (ftrace.bucket_range && !ftrace.min_latency) {
 			/* default min latency should be the bucket range */
 			ftrace.min_latency = ftrace.bucket_range;
 		}
@@ -1749,7 +1751,7 @@ int cmd_ftrace(int argc, const char **argv)
 			ret = -EINVAL;
 			goto out_delete_filters;
 		}
-		if (!ftrace.max_latency) {
+		if (ftrace.bucket_range && !ftrace.max_latency) {
 			/* default max latency should depend on bucket range and num_buckets */
 			ftrace.max_latency = (NUM_BUCKET - 2) * ftrace.bucket_range +
 						ftrace.min_latency;