[PATCH v3] selftests/resctrl: Print a message if the result of MBM&CMT tests is failed on Intel cpu

[Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>]

According to "Intel Resource Director Technology (Intel RDT) on 
2nd Generation Intel Xeon Scalable Processors Reference Manual",
When the Intel Sub-NUMA Clustering(SNC) feature is enabled,
Intel CMT and MBM counters may not be accurate.

However, there does not seem to be an architectural way to detect
if SNC is enabled.

If the result of MBM&CMT test fails on Intel CPU,
print a message to let users know a possible cause of failure.

Signed-off-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
---
Hello,

In PATCH V2, I tried to detect whether SNC is enabled by NUMA info and
cpuinfo(socket_num), but it is not reliable and no future-proof.

I just print a message to let users know a possible cause of "not ok",
When CMT or MBM test runs on Intel CPU, and the result is "not ok".

This patch is based on v5.16.

 tools/testing/selftests/resctrl/resctrl_tests.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
index 973f09a66e1e..ec2bdce7b85f 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -14,8 +14,9 @@
 #define BENCHMARK_ARG_SIZE	64
 
 bool is_amd;
+bool is_intel;
 
-void detect_amd(void)
+void detect_vendor(void)
 {
 	FILE *inf = fopen("/proc/cpuinfo", "r");
 	char *res;
@@ -29,6 +30,7 @@ void detect_amd(void)
 		char *s = strchr(res, ':');
 
 		is_amd = s && !strcmp(s, ": AuthenticAMD\n");
+		is_intel = s && !strcmp(s, ": GenuineIntel\n");
 		free(res);
 	}
 	fclose(inf);
@@ -70,6 +72,8 @@ static void run_mbm_test(bool has_ben, char **benchmark_cmd, int span,
 		sprintf(benchmark_cmd[5], "%s", MBA_STR);
 	res = mbm_bw_change(span, cpu_no, bw_report, benchmark_cmd);
 	ksft_test_result(!res, "MBM: bw change\n");
+	if (is_intel && res)
+		ksft_print_msg("Intel CMT and MBM counters may be inaccurate when Sub-NUMA Clustering (SNC) is enabled. Ensure SNC is disabled in the BIOS if this system supports SNC.\n");
 	mbm_test_cleanup();
 }
 
@@ -106,6 +110,8 @@ static void run_cmt_test(bool has_ben, char **benchmark_cmd, int cpu_no)
 		sprintf(benchmark_cmd[5], "%s", CMT_STR);
 	res = cmt_resctrl_val(cpu_no, 5, benchmark_cmd);
 	ksft_test_result(!res, "CMT: test\n");
+	if (is_intel && res)
+		ksft_print_msg("Intel CMT and MBM counters may be inaccurate when Sub-NUMA Clustering (SNC) is enabled. Ensure SNC is disabled in the BIOS if this system supports SNC.\n");
 	cmt_test_cleanup();
 }
 
@@ -207,8 +213,8 @@ int main(int argc, char **argv)
 	if (geteuid() != 0)
 		return ksft_exit_fail_msg("Not running as root, abort testing.\n");
 
-	/* Detect AMD vendor */
-	detect_amd();
+	/* Detect AMD/INTEL vendor */
+	detect_vendor();
 
 	if (has_ben) {
 		/* Extract benchmark command from command line. */
-- 
2.27.0