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From:   =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
To:     Fenghua Yu <fenghua.yu@intel.com>,
        Reinette Chatre <reinette.chatre@intel.com>,
        Shuah Khan <shuah@kernel.org>,
        Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>,
        =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: [PATCH 1/1] selftests/resctrl: Don't fail MBM test when schemata doesn't support MB:x=x line
Date:   Tue, 17 Oct 2023 15:17:50 +0300
Message-Id: <20231017121750.15433-1-ilpo.jarvinen@linux.intel.com>
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Commit 20d96b25cc4c ("selftests/resctrl: Fix schemata write error
check") exposed a problem in feature detection logic in MBM selftest.
If schemata does not support MB:x=x entries, the schemata write to
initialize 100% memory bandwidth allocation in mbm_setup() will now
fail with -EINVAL due to the error handling corrected by 20d96b25cc4c.
Commit 20d96b25cc4c just uncovers the failed write, it is not wrong
itself.

If MB:x=x is not supported by schemata, it is safe to assume 100%
memory bandwidth is always set. Therefore, the previously ignored error
does not make the MBM test itself wrong.

Restore the previous behavior of MBM test by checking MB support before
attempting to write it into schemata which results in behavior
equivalent to ignoring the write error.

Fixes: 20d96b25cc4c ("selftests/resctrl: Fix schemata write error check")
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 tools/testing/selftests/resctrl/mbm_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c
index d3c0d30c676a..85987957e7f5 100644
--- a/tools/testing/selftests/resctrl/mbm_test.c
+++ b/tools/testing/selftests/resctrl/mbm_test.c
@@ -95,7 +95,7 @@ static int mbm_setup(struct resctrl_val_param *p)
 		return END_OF_TESTS;
 
 	/* Set up shemata with 100% allocation on the first run. */
-	if (p->num_of_runs == 0)
+	if ((p->num_of_runs == 0) && validate_resctrl_feature_request("MB", NULL))
 		ret = write_schemata(p->ctrlgrp, "100", p->cpu_no,
 				     p->resctrl_val);
 
-- 
2.30.2