Re: [PATCH v2] selftests: powerpc: Fix CPU affinity for child process

On systems with large number of cpus, test fails trying to set
affinity for child process by calling sched_setaffinity() with 
smaller size for cpuset. This patch fixes it by making sure that
the size of allocated cpu set is dependent on the number of CPUs
as reported by get_nprocs().

Fixes: 00b7ec5c9cf3 ("selftests/powerpc: Import Anton's context_switch2 benchmark")
Reported-by: Shirisha Ganta <redacted>
Signed-off-by: Harish <redacted>
Signed-off-by: Sandipan Das <redacted>
---
 .../powerpc/benchmarks/context_switch.c        | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/powerpc/benchmarks/context_switch.c b/tools/testing/selftests/powerpc/benchmarks/context_switch.c
index a2e8c9da7fa5..de6c49d6f88f 100644
--- a/tools/testing/selftests/powerpc/benchmarks/context_switch.c
+++ b/tools/testing/selftests/powerpc/benchmarks/context_switch.c

@@ -19,6 +19,7 @@
 #include <limits.h>
 #include <sys/time.h>
 #include <sys/syscall.h>
+#include <sys/sysinfo.h>
 #include <sys/types.h>
 #include <sys/shm.h>
 #include <linux/futex.h>

@@ -104,8 +105,9 @@ static void start_thread_on(void *(*fn)(void *), void *arg, unsigned long cpu)

 static void start_process_on(void *(*fn)(void *), void *arg, unsigned long cpu)
 {
-	int pid;
-	cpu_set_t cpuset;
+	int pid, ncpus;
+	cpu_set_t *cpuset;
+	size_t size;

 	pid = fork();
 	if (pid == -1) {

@@ -116,12 +118,16 @@ static void start_process_on(void *(*fn)(void *), void *arg, unsigned long cpu)
 	if (pid)
 		return;

-	CPU_ZERO(&cpuset);
-	CPU_SET(cpu, &cpuset);
+	size = CPU_ALLOC_SIZE(ncpus);
+	ncpus = get_nprocs();
+	cpuset = CPU_ALLOC(ncpus);

+	CPU_ZERO_S(size, cpuset);
+	CPU_SET_S(cpu, size, cpuset);

-	if (sched_setaffinity(0, sizeof(cpuset), &cpuset)) {
+	if (sched_setaffinity(0, size, cpuset)) {
 		perror("sched_setaffinity");
-		exit(1);
+		CPU_FREE(cpuset);
+		exit(-1);
 	}