[PATCH V3 1/2] tools/perf: Fix perf bench numa testcase to check if CPU used to bind task is online

[Athira Rajeev]

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

Tested-by: Disha Goel <disgoel@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
Reported-by: Disha Goel <disgoel@xxxxxxxxxxxxxxxxxx>
---
Changelog
 The first version was posted here:
 https://lore.kernel.org/all/20220406175113.87881-5-atrajeev@xxxxxxxxxxxxxxxxxx/
 This v3 version separates patch 4 and addressing review comments
 from Arnaldo to use sysfs__read_str for reading sysfs file.

 tools/perf/bench/numa.c  |  8 +++++--
 tools/perf/util/header.c | 51 ++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/header.h |  1 +
 3 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/tools/perf/bench/numa.c b/tools/perf/bench/numa.c
index f2640179ada9..c838c248aa2c 100644
--- a/tools/perf/bench/numa.c
+++ b/tools/perf/bench/numa.c
@@ -34,6 +34,7 @@
 #include <linux/numa.h>
 #include <linux/zalloc.h>
 
+#include "../util/header.h"
 #include <numa.h>
 #include <numaif.h>
 
@@ -585,6 +586,11 @@ static int parse_setup_cpu_list(void)
 			return -1;
 		}
 
+		if (is_cpu_online(bind_cpu_0) != 1 || is_cpu_online(bind_cpu_1) != 1) {
+			printf("\nTest not applicable, bind_cpu_0 or bind_cpu_1 is offline\n");
+			return -1;
+		}
+
 		BUG_ON(bind_cpu_0 < 0 || bind_cpu_1 < 0);
 		BUG_ON(bind_cpu_0 > bind_cpu_1);
 
@@ -752,8 +758,6 @@ static int parse_nodes_opt(const struct option *opt __maybe_unused,
 	return parse_node_list(arg);
 }
 
-#define BIT(x) (1ul << x)
-
 static inline uint32_t lfsr_32(uint32_t lfsr)
 {
 	const uint32_t taps = BIT(1) | BIT(5) | BIT(6) | BIT(31);
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)
diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
index c9e3265832d9..0eb4bc29a5a4 100644
--- a/tools/perf/util/header.h
+++ b/tools/perf/util/header.h
@@ -158,6 +158,7 @@ int do_write(struct feat_fd *fd, const void *buf, size_t size);
 int write_padded(struct feat_fd *fd, const void *bf,
 		 size_t count, size_t count_aligned);
 
+int is_cpu_online(unsigned int cpu);
 /*
  * arch specific callback
  */
-- 
2.35.1