[PATCH] selftests/bpf: skip get_branch_snapshot in vm

VMs running on latest kernel support LBR. However, bpf_get_branch_snapshot
couldn't stop the LBR before too many entries are flushed. Skip the test
for VMs before we find a proper fix for VMs.

Read the "flags" line from /proc/cpuinfo, if it contains "hypervisor",
skip test get_branch_snapshot.

Fixes: 025bd7c753aa (selftests/bpf: Add test for bpf_get_branch_snapshot)
Signed-off-by: Song Liu <redacted>
---
 .../bpf/prog_tests/get_branch_snapshot.c      | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
index 67e86f8d86775..bf9d47a859449 100644
--- a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
+++ b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c

@@ -6,6 +6,30 @@
 static int *pfd_array;
 static int cpu_cnt;
 
+static bool is_hypervisor(void)
+{
+	char *line = NULL;
+	bool ret = false;
+	size_t len;
+	FILE *fp;
+
+	fp = fopen("/proc/cpuinfo", "r");
+	if (!fp)
+		return false;
+
+	while (getline(&line, &len, fp) != -1) {
+		if (strstr(line, "flags") == line) {
+			if (strstr(line, "hypervisor") != NULL)
+				ret = true;
+			break;
+		}
+	}
+
+	free(line);
+	fclose(fp);
+	return ret;
+}
+
 static int create_perf_events(void)
 {
 	struct perf_event_attr attr = {0};

@@ -54,6 +78,14 @@ void test_get_branch_snapshot(void)
 	struct get_branch_snapshot *skel = NULL;
 	int err;
 
+	if (is_hypervisor()) {
+		/* As of today, LBR in hypervisor cannot be stopped before
+		 * too many entries are flushed. Skip the test for now in
+		 * hypervisor until we optimize the LBR in hypervisor.
+		 */
+		test__skip();
+		return;
+	}
 	if (create_perf_events()) {
 		test__skip();  /* system doesn't support LBR */
 		goto cleanup;

-- 
2.30.2

On Wed, Oct 6, 2021 at 1:32 PM Song Liu [off-list ref] wrote:

VMs running on latest kernel support LBR. However, bpf_get_branch_snapshot
couldn't stop the LBR before too many entries are flushed. Skip the test
for VMs before we find a proper fix for VMs.

Read the "flags" line from /proc/cpuinfo, if it contains "hypervisor",
skip test get_branch_snapshot.

Forgot to use --subject-prefix. This applies to bpf-next.

Thanks,
Song

On Wed, Oct 6, 2021 at 1:31 PM Song Liu [off-list ref] wrote:

VMs running on latest kernel support LBR. However, bpf_get_branch_snapshot
couldn't stop the LBR before too many entries are flushed. Skip the test
for VMs before we find a proper fix for VMs.

Read the "flags" line from /proc/cpuinfo, if it contains "hypervisor",
skip test get_branch_snapshot.

Fixes: 025bd7c753aa (selftests/bpf: Add test for bpf_get_branch_snapshot)

missing quotes?

strncmp() would be more explicit. That's what you are trying to do
(prefix match), right?

On Wed, Oct 6, 2021 at 2:36 PM Andrii Nakryiko
[off-list ref] wrote:

On Wed, Oct 6, 2021 at 1:31 PM Song Liu [off-list ref] wrote:

quoted

VMs running on latest kernel support LBR. However, bpf_get_branch_snapshot
couldn't stop the LBR before too many entries are flushed. Skip the test
for VMs before we find a proper fix for VMs.

Read the "flags" line from /proc/cpuinfo, if it contains "hypervisor",
skip test get_branch_snapshot.

Fixes: 025bd7c753aa (selftests/bpf: Add test for bpf_get_branch_snapshot)

missing quotes?

Aha, I copied this line from e31eec77e4ab90dcec7d2da93415f839098dc287. Will fix.

quoted

Signed-off-by: Song Liu <redacted>
---
 .../bpf/prog_tests/get_branch_snapshot.c      | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
index 67e86f8d86775..bf9d47a859449 100644
--- a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
+++ b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c

@@ -6,6 +6,30 @@
 static int *pfd_array;
 static int cpu_cnt;

+static bool is_hypervisor(void)
+{
+       char *line = NULL;
+       bool ret = false;
+       size_t len;
+       FILE *fp;
+
+       fp = fopen("/proc/cpuinfo", "r");
+       if (!fp)
+               return false;
+
+       while (getline(&line, &len, fp) != -1) {
+               if (strstr(line, "flags") == line) {

strncmp() would be more explicit. That's what you are trying to do
(prefix match), right?

right... let me fix it in v2.

quoted

+                       if (strstr(line, "hypervisor") != NULL)
+                               ret = true;
+                       break;
+               }
+       }
+
+       free(line);
+       fclose(fp);
+       return ret;
+}
+
 static int create_perf_events(void)
 {
        struct perf_event_attr attr = {0};

@@ -54,6 +78,14 @@ void test_get_branch_snapshot(void)
        struct get_branch_snapshot *skel = NULL;
        int err;

+       if (is_hypervisor()) {
+               /* As of today, LBR in hypervisor cannot be stopped before
+                * too many entries are flushed. Skip the test for now in
+                * hypervisor until we optimize the LBR in hypervisor.
+                */
+               test__skip();
+               return;
+       }
        if (create_perf_events()) {
                test__skip();  /* system doesn't support LBR */
                goto cleanup;
--

2.30.2