Re: [PATCH 1/2] KVM: selftests: Allow >1 guest mode in access_tracking_perf_test

From: Sean Christopherson
Date: Mon Nov 14 2022 - 12:12:57 EST

On Fri, Nov 11, 2022, Oliver Upton wrote:
> As the name implies, for_each_guest_mode() will run the test case for
> all supported guest addressing modes. On x86 that doesn't amount to
> anything, but arm64 can handle 4K, 16K, and 64K page sizes on supporting
> hardware.
>
> Blindly attempting to run access_tracking_perf_test on arm64 stalls on
> the second test case, as the 'done' global remains set between test
> iterations. Clear it after VM teardown in anticipation of a subsequent
> test case.
>
> Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
> ---
> tools/testing/selftests/kvm/access_tracking_perf_test.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> index 76c583a07ea2..4da066479e0a 100644
> --- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
> +++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> @@ -326,6 +326,9 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>
> perf_test_join_vcpu_threads(nr_vcpus);
> perf_test_destroy_vm(vm);
> +
> + /* Clear done in anticipation of testing another guest mode */
> + done = false;

Can we fix this in the so called "perf_test" infrastructure?
memslot_modification_stress_test.c has the same bug just inverted (see run_vcpus).

E.g. (compile tested only)

---
.../selftests/kvm/access_tracking_perf_test.c | 28 +++++--------------
.../selftests/kvm/include/perf_test_util.h | 3 ++
.../selftests/kvm/lib/perf_test_util.c | 3 ++
.../kvm/memslot_modification_stress_test.c | 6 +---
4 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
index 76c583a07ea2..786bc62a2c79 100644
--- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
+++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
@@ -58,9 +58,6 @@ static enum {
ITERATION_MARK_IDLE,
} iteration_work;

-/* Set to true when vCPU threads should exit. */
-static bool done;
-
/* The iteration that was last completed by each vCPU. */
static int vcpu_last_completed_iteration[KVM_MAX_VCPUS];

@@ -206,28 +203,20 @@ static void assert_ucall(struct kvm_vcpu *vcpu, uint64_t expected_ucall)
expected_ucall, actual_ucall);
}

-static bool spin_wait_for_next_iteration(int *current_iteration)
-{
- int last_iteration = *current_iteration;
-
- do {
- if (READ_ONCE(done))
- return false;
-
- *current_iteration = READ_ONCE(iteration);
- } while (last_iteration == *current_iteration);
-
- return true;
-}
-
static void vcpu_thread_main(struct perf_test_vcpu_args *vcpu_args)
{
struct kvm_vcpu *vcpu = vcpu_args->vcpu;
struct kvm_vm *vm = perf_test_args.vm;
int vcpu_idx = vcpu_args->vcpu_idx;
int current_iteration = 0;
+ int last_iteration;
+
+ while (!READ_ONCE(perf_test_args.stop_vcpus)) {
+ last_iteration = current_iteration;
+ do {
+ current_iteration = READ_ONCE(iteration);
+ } while (current_iteration == last_iteration);

- while (spin_wait_for_next_iteration(&current_iteration)) {
switch (READ_ONCE(iteration_work)) {
case ITERATION_ACCESS_MEMORY:
vcpu_run(vcpu);
@@ -321,9 +310,6 @@ static void run_test(enum vm_guest_mode mode, void *arg)
mark_memory_idle(vm, nr_vcpus);
access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from idle memory");

- /* Set done to signal the vCPU threads to exit */
- done = true;
-
perf_test_join_vcpu_threads(nr_vcpus);
perf_test_destroy_vm(vm);
}
diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h
index eaa88df0555a..536d7c3c3f14 100644
--- a/tools/testing/selftests/kvm/include/perf_test_util.h
+++ b/tools/testing/selftests/kvm/include/perf_test_util.h
@@ -40,6 +40,9 @@ struct perf_test_args {
/* Run vCPUs in L2 instead of L1, if the architecture supports it. */
bool nested;

+ /* Test is done, stop running vCPUs. */
+ bool stop_vcpus;
+
struct perf_test_vcpu_args vcpu_args[KVM_MAX_VCPUS];
};

diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
index 9618b37c66f7..ee3f499ccbd2 100644
--- a/tools/testing/selftests/kvm/lib/perf_test_util.c
+++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
@@ -267,6 +267,7 @@ void perf_test_start_vcpu_threads(int nr_vcpus,

vcpu_thread_fn = vcpu_fn;
WRITE_ONCE(all_vcpu_threads_running, false);
+ WRITE_ONCE(perf_test_args.stop_vcpus, false);

for (i = 0; i < nr_vcpus; i++) {
struct vcpu_thread *vcpu = &vcpu_threads[i];
@@ -289,6 +290,8 @@ void perf_test_join_vcpu_threads(int nr_vcpus)
{
int i;

+ WRITE_ONCE(perf_test_args.stop_vcpus, true);
+
for (i = 0; i < nr_vcpus; i++)
pthread_join(vcpu_threads[i].thread, NULL);
}
diff --git a/tools/testing/selftests/kvm/memslot_modification_stress_test.c b/tools/testing/selftests/kvm/memslot_modification_stress_test.c
index bb1d17a1171b..3a5e4518307c 100644
--- a/tools/testing/selftests/kvm/memslot_modification_stress_test.c
+++ b/tools/testing/selftests/kvm/memslot_modification_stress_test.c
@@ -34,8 +34,6 @@
static int nr_vcpus = 1;
static uint64_t guest_percpu_mem_size = DEFAULT_PER_VCPU_MEM_SIZE;

-static bool run_vcpus = true;
-
static void vcpu_worker(struct perf_test_vcpu_args *vcpu_args)
{
struct kvm_vcpu *vcpu = vcpu_args->vcpu;
@@ -45,7 +43,7 @@ static void vcpu_worker(struct perf_test_vcpu_args *vcpu_args)
run = vcpu->run;

/* Let the guest access its memory until a stop signal is received */
- while (READ_ONCE(run_vcpus)) {
+ while (!READ_ONCE(perf_test_args.stop_vcpus)) {
ret = _vcpu_run(vcpu);
TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);

@@ -110,8 +108,6 @@ static void run_test(enum vm_guest_mode mode, void *arg)
add_remove_memslot(vm, p->memslot_modification_delay,
p->nr_memslot_modifications);

- run_vcpus = false;
-
perf_test_join_vcpu_threads(nr_vcpus);
pr_info("All vCPU threads joined\n");


base-commit: 10dbc57b5777e6938a648eb4a870bad448fcb6f5
--