perf test: Add a runs-per-test flag

To detect flakes it is useful to run tests more than once. Add a
runs-per-test flag that will run each test multiple times. Example
output:

```
$ perf test -r 3 lbr -v
122: perf record LBR tests                                           : Ok
122: perf record LBR tests                                           : Ok
122: perf record LBR tests                                           : Ok
```

Update the documentation for the runs-per-test option.

Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20250110045736.598281-5-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Author: captain5050

tools/perf/Documentation/perf-test.txt

@@ -37,6 +37,11 @@ OPTIONS
 	tests are run sequentially, but other tests are run in
 	parallel to speed execution.
 
+-r::
+--runs-per-test::
+	Run each test the given number of times, by default once. This
+	option can be useful to determine if a test is flaky.
+
 -F::
 --dont-fork::
 	Do not fork child for each test, run all tests within single process, this

tools/perf/tests/builtin-test.c

@@ -42,6 +42,8 @@
 static bool dont_fork;
 /* Fork the tests in parallel and wait for their completion. */
 static bool sequential;
+/* Number of times each test is run. */
+static unsigned int runs_per_test = 1;
 const char *dso_to_test;
 const char *test_objdump_path = "objdump";
 
@@ -485,7 +487,7 @@ static int __cmd_test(struct test_suite **suites, int argc, const char *argv[],
 			len = strlen(test_description(*t, i));
 			if (width < len)
 				width = len;
-			num_tests++;
+			num_tests += runs_per_test;
 		}
 	}
 	child_tests = calloc(num_tests, sizeof(*child_tests));
@@ -549,16 +551,18 @@ static int __cmd_test(struct test_suite **suites, int argc, const char *argv[],
 				continue;
 			}
 
-			test_suite__for_each_test_case(*t, curr_test_case) {
-				if (!perf_test__matches(test_description(*t, curr_test_case),
-							curr_suite, argc, argv))
-					continue;
-
-				err = start_test(*t, curr_suite, curr_test_case,
-						 &child_tests[child_test_num++],
-						 width, pass);
-				if (err)
-					goto err_out;
+			for (unsigned int run = 0; run < runs_per_test; run++) {
+				test_suite__for_each_test_case(*t, curr_test_case) {
+					if (!perf_test__matches(test_description(*t, curr_test_case),
+								curr_suite, argc, argv))
+						continue;
+
+					err = start_test(*t, curr_suite, curr_test_case,
+							 &child_tests[child_test_num++],
+							 width, pass);
+					if (err)
+						goto err_out;
+				}
 			}
 		}
 		if (!sequential) {
@@ -698,6 +702,8 @@ int cmd_test(int argc, const char **argv)
 		    "Do not fork for testcase"),
 	OPT_BOOLEAN('S', "sequential", &sequential,
 		    "Run the tests one after another rather than in parallel"),
+	OPT_UINTEGER('r', "runs-per-test", &runs_per_test,
+		     "Run each test the given number of times, default 1"),
 	OPT_STRING('w', "workload", &workload, "work", "workload to run for testing, use '--list-workloads' to list the available ones."),
 	OPT_BOOLEAN(0, "list-workloads", &list_workloads, "List the available builtin workloads to use with -w/--workload"),
 	OPT_STRING(0, "dso", &dso_to_test, "dso", "dso to test"),