perf bench: Fix numa testcase to check if CPU used to bind task is online

Perf numa bench test fails with error:

Testcase:

  ./perf bench numa mem -p 2 -t 1 -P 1024 -C 0,8 -M 1,0 -s 20 -zZq --thp  1 --no-data_rand_walk

Failure snippet:

<<>>
  Running 'numa/mem' benchmark:

  # Running main, "perf bench numa numa-mem -p 2 -t 1 -P 1024 -C 0,8 -M 1,0 -s 20 -zZq --thp 1 --no-data_rand_walk"

  perf: bench/numa.c:333: bind_to_cpumask: Assertion `!(ret)' failed.
<<>>

The Testcases uses CPU's 0 and 8. In function "parse_setup_cpu_list",
There is check to see if cpu number is greater than max cpu's possible
in the system ie via "if (bind_cpu_0 >= g->p.nr_cpus || bind_cpu_1 >=
g->p.nr_cpus) {".

But it could happen that system has say 48 CPU's, but only number of
online CPU's is 0-7. Other CPU's are offlined. Since "g->p.nr_cpus" is
48, so function will go ahead and set bit for CPU 8 also in cpumask (
td->bind_cpumask).

bind_to_cpumask function is called to set affinity using
sched_setaffinity and the cpumask. Since the CPU8 is not present, set
affinity will fail here with EINVAL.

Fix this issue by adding a check to make sure that, CPU's provided in
the input argument values are online before proceeding further and skip
the test. For this, include new helper function "is_cpu_online" in
"tools/perf/util/header.c".

Since "BIT(x)" definition will get included from header.h, remove
that from bench/numa.c

Reported-by: Disha Goel <disgoel@linux.vnet.ibm.com>
Signed-off-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Tested-by: Disha Goel <disgoel@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nageswara R Sastry <rnsastry@linux.ibm.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20220412164059.42654-2-atrajeev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index d546ff724dbe..a27132e5a5ef 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -983,6 +983,57 @@ static int write_dir_format(struct feat_fd *ff,
 	return do_write(ff, &data->dir.version, sizeof(data->dir.version));
 }
 
+/*
+ * Check whether a CPU is online
+ *
+ * Returns:
+ *     1 -> if CPU is online
+ *     0 -> if CPU is offline
+ *    -1 -> error case
+ */
+int is_cpu_online(unsigned int cpu)
+{
+	char *str;
+	size_t strlen;
+	char buf[256];
+	int status = -1;
+	struct stat statbuf;
+
+	snprintf(buf, sizeof(buf),
+		"/sys/devices/system/cpu/cpu%d", cpu);
+	if (stat(buf, &statbuf) != 0)
+		return 0;
+
+	/*
+	 * Check if /sys/devices/system/cpu/cpux/online file
+	 * exists. Some cases cpu0 won't have online file since
+	 * it is not expected to be turned off generally.
+	 * In kernels without CONFIG_HOTPLUG_CPU, this
+	 * file won't exist
+	 */
+	snprintf(buf, sizeof(buf),
+		"/sys/devices/system/cpu/cpu%d/online", cpu);
+	if (stat(buf, &statbuf) != 0)
+		return 1;
+
+	/*
+	 * Read online file using sysfs__read_str.
+	 * If read or open fails, return -1.
+	 * If read succeeds, return value from file
+	 * which gets stored in "str"
+	 */
+	snprintf(buf, sizeof(buf),
+		"devices/system/cpu/cpu%d/online", cpu);
+
+	if (sysfs__read_str(buf, &str, &strlen) < 0)
+		return status;
+
+	status = atoi(str);
+
+	free(str);
+	return status;
+}
+
 #ifdef HAVE_LIBBPF_SUPPORT
 static int write_bpf_prog_info(struct feat_fd *ff,
 			       struct evlist *evlist __maybe_unused)