selftests/resctrl: Remove "once" parameter required to be false

The CMT, MBM, and MBA tests rely on a benchmark that runs while
the test makes changes to needed configuration (for example memory
bandwidth allocation) and takes needed measurements. By default
the "fill_buf" benchmark is used and by default (via its
"once = false" setting) "fill_buf" is configured to run until
terminated after the test completes.

An unintended consequence of enabling the user to override the
benchmark also enables the user to change parameters to the
"fill_buf" benchmark. This enables the user to set "fill_buf" to
only cycle through the buffer once (by setting "once = true")
and thus breaking the CMT, MBA, and MBM tests that expect
workload/interference to be reflected by their measurements.

Prevent user space from changing the "once" parameter and ensure
that it is always false for the CMT, MBA, and MBM tests.

Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
index ecbb7605a981..e7878077883f 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -266,8 +266,13 @@ last_arg:
 		uparams.benchmark_cmd[1] = span_str;
 		uparams.benchmark_cmd[2] = "1";
 		uparams.benchmark_cmd[3] = "0";
-		uparams.benchmark_cmd[4] = "false";
-		uparams.benchmark_cmd[5] = NULL;
+		/*
+		 * Fourth parameter was previously used to indicate
+		 * how long "fill_buf" should run for, with "false"
+		 * ("fill_buf" will keep running until terminated)
+		 * the only option that works.
+		 */
+		uparams.benchmark_cmd[4] = NULL;
 	}
 
 	ksft_set_plan(tests);