KVM: selftests: Pre-set threads affinity in hardware disable test when possible

When building against a libc that provides pthread_attr_setaffinity_np(),
pre-set the grandchildren threads CPU affinity in the hardware disable test
to further reduce the perceived latency of pthread_create().  On large NUMA
systems, this reduces the average runtime from ~10s to ~5s.

Link: https://patch.msgid.link/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

tools/testing/selftests/kvm/hardware_disable_test.c

@@ -36,7 +36,9 @@ static void *run_vcpu(void *arg)
 	struct kvm_vcpu *vcpu = arg;
 	struct kvm_run *run = vcpu->run;
 
+#ifndef _GNU_SOURCE
 	kvm_sched_setaffinity(0, sizeof(cpu_set_t), &threads_cpu_set);
+#endif
 
 	vcpu_run(vcpu);
 
@@ -50,7 +52,9 @@ static void *sleeping_thread(void *arg)
 {
 	int fd;
 
+#ifndef _GNU_SOURCE
 	kvm_sched_setaffinity(0, sizeof(cpu_set_t), &threads_cpu_set);
+#endif
 
 	while (true) {
 		fd = open("/dev/null", O_RDWR);
@@ -80,22 +84,28 @@ static inline void check_join(pthread_t thread, void **retval)
 static void run_test(u32 run)
 {
 	struct kvm_vcpu *vcpu;
+	pthread_attr_t attr;
 	struct kvm_vm *vm;
 	pthread_t threads[VCPU_NUM];
 	pthread_t throw_away;
 	void *b;
 	u32 i, j;
 
+	TEST_ASSERT_EQ(pthread_attr_init(&attr), 0);
+#ifdef _GNU_SOURCE
+	TEST_ASSERT_EQ(pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &threads_cpu_set), 0);
+#endif
+
 	vm = vm_create(VCPU_NUM);
 
 	pr_debug("%s: [%d] start vcpus\n", __func__, run);
 	for (i = 0; i < VCPU_NUM; ++i) {
 		vcpu = vm_vcpu_add(vm, i, guest_code);
 
-		check_create_thread(&threads[i], NULL, run_vcpu, vcpu);
+		check_create_thread(&threads[i], &attr, run_vcpu, vcpu);
 
 		for (j = 0; j < SLEEPING_THREAD_NUM; ++j) {
-			check_create_thread(&throw_away, NULL, sleeping_thread,
+			check_create_thread(&throw_away, &attr, sleeping_thread,
 					    (void *)NULL);
 		}
 	}