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

[Oliver Upton <oliver.upton@linux.dev>]

On Mon, Nov 14, 2022 at 05:12:48PM +0000, Sean Christopherson wrote:
> 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@linux.dev>
> > ---
> >  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).

Yeah, sounds good to me. I'll wrap your diff up in a patch here in a
bit.

--
Thanks,
Oliver

> ---
>  .../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
> -- 
>