[PATCH v2 02/12] KVM: selftests: Set threads CPU affinity before doing work in hardware disable test

[Sean Christopherson]

Affine worker threads to their target pCPU set *before* doing any work in
the hardware disable test.  When running a preemptible kernel on a NUMA
system with a large number of CPUs (100+ of CPUs), waiting to set the
affinity of the grandchildren until after the grandchild is fully spun up
results in total test runtimes of over a minute, presumably due to
cross-node NUMA penalties and scheduler lock contention.

E.g. from the perspective of the caller, when waiting to affine the tasks,
pthread_create() takes ~100x longer.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 .../selftests/kvm/hardware_disable_test.c     | 23 +++++++------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/tools/testing/selftests/kvm/hardware_disable_test.c b/tools/testing/selftests/kvm/hardware_disable_test.c
index 3147f5c97e94..f088b4af3ccc 100644
--- a/tools/testing/selftests/kvm/hardware_disable_test.c
+++ b/tools/testing/selftests/kvm/hardware_disable_test.c
@@ -21,6 +21,7 @@
 #define FORK_NUM (1ULL << 9)
 #define DELAY_US_MAX 2000
 
+static cpu_set_t threads_cpu_set;
 sem_t *sem;
 
 static void guest_code(void)
@@ -35,6 +36,8 @@ static void *run_vcpu(void *arg)
 	struct kvm_vcpu *vcpu = arg;
 	struct kvm_run *run = vcpu->run;
 
+	kvm_sched_setaffinity(0, sizeof(cpu_set_t), &threads_cpu_set);
+
 	vcpu_run(vcpu);
 
 	TEST_ASSERT(false, "%s: exited with reason %d: %s",
@@ -47,6 +50,8 @@ static void *sleeping_thread(void *arg)
 {
 	int fd;
 
+	kvm_sched_setaffinity(0, sizeof(cpu_set_t), &threads_cpu_set);
+
 	while (true) {
 		fd = open("/dev/null", O_RDWR);
 		close(fd);
@@ -64,14 +69,6 @@ static inline void check_create_thread(pthread_t *thread, pthread_attr_t *attr,
 	TEST_ASSERT(r == 0, "%s: failed to create thread", __func__);
 }
 
-static inline void check_set_affinity(pthread_t thread, cpu_set_t *cpu_set)
-{
-	int r;
-
-	r = pthread_setaffinity_np(thread, sizeof(cpu_set_t), cpu_set);
-	TEST_ASSERT(r == 0, "%s: failed set affinity", __func__);
-}
-
 static inline void check_join(pthread_t thread, void **retval)
 {
 	int r;
@@ -84,16 +81,11 @@ static void run_test(u32 run)
 {
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
-	cpu_set_t cpu_set;
 	pthread_t threads[VCPU_NUM];
 	pthread_t throw_away;
 	void *b;
 	u32 i, j;
 
-	CPU_ZERO(&cpu_set);
-	for (i = 0; i < VCPU_NUM; i++)
-		CPU_SET(i, &cpu_set);
-
 	vm = vm_create(VCPU_NUM);
 
 	pr_debug("%s: [%d] start vcpus\n", __func__, run);
@@ -101,12 +93,10 @@ static void run_test(u32 run)
 		vcpu = vm_vcpu_add(vm, i, guest_code);
 
 		check_create_thread(&threads[i], NULL, run_vcpu, vcpu);
-		check_set_affinity(threads[i], &cpu_set);
 
 		for (j = 0; j < SLEEPING_THREAD_NUM; ++j) {
 			check_create_thread(&throw_away, NULL, sleeping_thread,
 					    (void *)NULL);
-			check_set_affinity(throw_away, &cpu_set);
 		}
 	}
 	pr_debug("%s: [%d] all threads launched\n", __func__, run);
@@ -153,6 +143,9 @@ int main(int argc, char **argv)
 	int s, r;
 	pid_t pid;
 
+	for (i = 0; i < VCPU_NUM; i++)
+		CPU_SET(i, &threads_cpu_set);
+
 	sem = sem_open("vm_sem", O_CREAT | O_EXCL, 0644, 0);
 	sem_unlink("vm_sem");
 
-- 
2.55.0.508.g3f0d502094-goog