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KVM: selftests: Set threads CPU affinity before doing work in hardware disable test

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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.

Link: https://patch.msgid.link/20260731195612.2697986-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2026-07-31 12:56:02 -07:00
parent f766bf3d0a
commit 2887da61c4
1 changed files with 8 additions and 15 deletions
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23
tools/testing/selftests/kvm/hardware_disable_test.c
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@ -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");