Re: [REPOST PATCH 11/16] selftests: KVM: aarch64: Add vCPU migration test for PMU

Reiji Watanabe
2023-03-07T03:44:21Z

Hi Raghu,

On Tue, Feb 14, 2023 at 5:07 PM Raghavendra Rao Ananta
<rananta@google.com> wrote:
>
> Implement a stress test for KVM by frequently force-migrating the
> vCPU to random pCPUs in the system. This would validate the
> save/restore functionality of KVM and starting/stopping of
> PMU counters as necessary.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
> .../testing/selftests/kvm/aarch64/vpmu_test.c | 195 +++++++++++++++++-
> 1 file changed, 193 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/aarch64/vpmu_test.c b/tools/testing/selftests/kvm/aarch64/vpmu_test.c
> index 5c166df245589..0c9d801f4e602 100644
> --- a/tools/testing/selftests/kvm/aarch64/vpmu_test.c
> +++ b/tools/testing/selftests/kvm/aarch64/vpmu_test.c
> @@ -19,9 +19,15 @@
> * higher exception levels (EL2, EL3). Verify this functionality by
> * configuring and trying to count the events for EL2 in the guest.
> *
> + * 4. Since the PMU registers are per-cpu, stress KVM by frequently
> + * migrating the guest vCPU to random pCPUs in the system, and check
> + * if the vPMU is still behaving as expected.
> + *
> * Copyright (c) 2022 Google LLC.
> *
> */
> +#define _GNU_SOURCE
> +
> #include <kvm_util.h>
> #include <processor.h>
> #include <test_util.h>
> @@ -30,6 +36,11 @@
> #include <linux/arm-smccc.h>
> #include <linux/bitfield.h>
> #include <linux/bitmap.h>
> +#include <stdlib.h>
> +#include <pthread.h>
> +#include <sys/sysinfo.h>
> +
> +#include "delay.h"
>
> /* The max number of the PMU event counters (excluding the cycle counter) */
> #define ARMV8_PMU_MAX_GENERAL_COUNTERS (ARMV8_PMU_MAX_COUNTERS - 1)
> @@ -37,6 +48,8 @@
> /* The max number of event numbers that's supported */
> #define ARMV8_PMU_MAX_EVENTS 64
>
> +#define msecs_to_usecs(msec) ((msec) * 1000LL)
> +
> /*
> * The macros and functions below for reading/writing PMEV{CNTR,TYPER}<n>_EL0
> * were basically copied from arch/arm64/kernel/perf_event.c.
> @@ -265,6 +278,7 @@ enum test_stage {
> TEST_STAGE_COUNTER_ACCESS = 1,
> TEST_STAGE_KVM_EVENT_FILTER,
> TEST_STAGE_KVM_EVTYPE_FILTER,
> + TEST_STAGE_VCPU_MIGRATION,
> };
>
> struct guest_data {
> @@ -275,6 +289,19 @@ struct guest_data {
>
> static struct guest_data guest_data;
>
> +#define VCPU_MIGRATIONS_TEST_ITERS_DEF 1000
> +#define VCPU_MIGRATIONS_TEST_MIGRATION_FREQ_MS 2
> +
> +struct test_args {
> + int vcpu_migration_test_iter;
> + int vcpu_migration_test_migrate_freq_ms;
> +};
> +
> +static struct test_args test_args = {
> + .vcpu_migration_test_iter = VCPU_MIGRATIONS_TEST_ITERS_DEF,
> + .vcpu_migration_test_migrate_freq_ms = VCPU_MIGRATIONS_TEST_MIGRATION_FREQ_MS,
> +};
> +
> static void guest_sync_handler(struct ex_regs *regs)
> {
> uint64_t esr, ec;
> @@ -352,7 +379,6 @@ static bool pmu_event_is_supported(uint64_t event)
> GUEST_ASSERT_3(!(_tval & mask), _tval, mask, set_expected);\
> }
>
> -
> /*
> * Extra instructions inserted by the compiler would be difficult to compensate
> * for, so hand assemble everything between, and including, the PMCR accesses
> @@ -459,6 +485,13 @@ static void test_event_count(uint64_t event, int pmc_idx, bool expect_count)
> }
> }
>
> +static void test_basic_pmu_functionality(void)
> +{
> + /* Test events on generic and cycle counters */
> + test_instructions_count(0, true);
> + test_cycles_count(true);
> +}
> +
> /*
> * Check if @mask bits in {PMCNTEN,PMINTEN,PMOVS}{SET,CLR} registers
> * are set or cleared as specified in @set_expected.
> @@ -748,6 +781,16 @@ static void guest_evtype_filter_test(void)
> GUEST_ASSERT_2(cnt == 0, cnt, typer);
> }
>
> +static void guest_vcpu_migration_test(void)
> +{
> + /*
> + * While the userspace continuously migrates this vCPU to random pCPUs,
> + * run basic PMU functionalities and verify the results.
> + */
> + while (test_args.vcpu_migration_test_iter--)
> + test_basic_pmu_functionality();
> +}
> +
> static void guest_code(void)
> {
> switch (guest_data.test_stage) {
> @@ -760,6 +803,9 @@ static void guest_code(void)
> case TEST_STAGE_KVM_EVTYPE_FILTER:
> guest_evtype_filter_test();
> break;
> + case TEST_STAGE_VCPU_MIGRATION:
> + guest_vcpu_migration_test();
> + break;
> default:
> GUEST_ASSERT_1(0, guest_data.test_stage);
> }
> @@ -837,6 +883,7 @@ create_vpmu_vm(void *guest_code, struct kvm_pmu_event_filter *pmu_event_filters)
>
> vpmu_vm->vm = vm = vm_create(1);
> vm_init_descriptor_tables(vm);
> +
> /* Catch exceptions for easier debugging */
> for (ec = 0; ec < ESR_EC_NUM; ec++) {
> vm_install_sync_handler(vm, VECTOR_SYNC_CURRENT, ec,
> @@ -881,6 +928,8 @@ static void run_vcpu(struct kvm_vcpu *vcpu)
> struct ucall uc;
>
> sync_global_to_guest(vcpu->vm, guest_data);
> + sync_global_to_guest(vcpu->vm, test_args);
> +
> vcpu_run(vcpu);
> switch (get_ucall(vcpu, &uc)) {
> case UCALL_ABORT:
> @@ -1098,11 +1147,112 @@ static void run_kvm_evtype_filter_test(void)
> destroy_vpmu_vm(vpmu_vm);
> }
>
> +struct vcpu_migrate_data {
> + struct vpmu_vm *vpmu_vm;
> + pthread_t *pt_vcpu;

Nit: Originally, I wasn't sure what 'pt' stands for.
Also, the 'pt_vcpu' made me think this would be a pointer to a vCPU.
Perhaps renaming this to 'vcpu_pthread' might be more clear ?

> + bool vcpu_done;
> +};
> +
> +static void *run_vcpus_migrate_test_func(void *arg)
> +{
> + struct vcpu_migrate_data *migrate_data = arg;
> + struct vpmu_vm *vpmu_vm = migrate_data->vpmu_vm;
> +
> + run_vcpu(vpmu_vm->vcpu);
> + migrate_data->vcpu_done = true;
> +
> + return NULL;
> +}
> +
> +static uint32_t get_pcpu(void)
> +{
> + uint32_t pcpu;
> + unsigned int nproc_conf;
> + cpu_set_t online_cpuset;
> +
> + nproc_conf = get_nprocs_conf();
> + sched_getaffinity(0, sizeof(cpu_set_t), &online_cpuset);
> +
> + /* Randomly find an available pCPU to place the vCPU on */
> + do {
> + pcpu = rand() % nproc_conf;
> + } while (!CPU_ISSET(pcpu, &online_cpuset));
> +
> + return pcpu;
> +}
> +
> +static int migrate_vcpu(struct vcpu_migrate_data *migrate_data)

Nit: You might want to pass a pthread_t rather than migrate_data
unless the function uses some more fields of the data in the
following patches.

> +{
> + int ret;
> + cpu_set_t cpuset;
> + uint32_t new_pcpu = get_pcpu();
> +
> + CPU_ZERO(&cpuset);
> + CPU_SET(new_pcpu, &cpuset);
> +
> + pr_debug("Migrating vCPU to pCPU: %u\n", new_pcpu);
> +
> + ret = pthread_setaffinity_np(*migrate_data->pt_vcpu, sizeof(cpuset), &cpuset);
> +
> + /* Allow the error where the vCPU thread is already finished */
> + TEST_ASSERT(ret == 0 || ret == ESRCH,
> + "Failed to migrate the vCPU to pCPU: %u; ret: %d\n", new_pcpu, ret);
> +
> + return ret;
> +}
> +
> +static void *vcpus_migrate_func(void *arg)
> +{
> + struct vcpu_migrate_data *migrate_data = arg;
> +
> + while (!migrate_data->vcpu_done) {
> + usleep(msecs_to_usecs(test_args.vcpu_migration_test_migrate_freq_ms));
> + migrate_vcpu(migrate_data);
> + }
> +
> + return NULL;
> +}
> +
> +static void run_vcpu_migration_test(uint64_t pmcr_n)
> +{
> + int ret;
> + struct vpmu_vm *vpmu_vm;
> + pthread_t pt_vcpu, pt_sched;
> + struct vcpu_migrate_data migrate_data = {
> + .pt_vcpu = &pt_vcpu,
> + .vcpu_done = false,
> + };
> +
> + __TEST_REQUIRE(get_nprocs() >= 2, "At least two pCPUs needed for vCPU migration test");

Considering that get_pcpu() chooses the target CPU from CPUs returned
from sched_getaffinity(), I would think the test should use the number of
the bits set in the returned cpu_set_t from sched_getaffinity() here
instead of get_nprocs(), as those numbers could be different (e.g. if the
test runs with taskset with a subset of the CPUs on the system).

> +
> + guest_data.test_stage = TEST_STAGE_VCPU_MIGRATION;
> + guest_data.expected_pmcr_n = pmcr_n;
> +
> + migrate_data.vpmu_vm = vpmu_vm = create_vpmu_vm(guest_code, NULL);
> +
> + /* Initialize random number generation for migrating vCPUs to random pCPUs */
> + srand(time(NULL));
> +
> + /* Spawn a vCPU thread */
> + ret = pthread_create(&pt_vcpu, NULL, run_vcpus_migrate_test_func, &migrate_data);
> + TEST_ASSERT(!ret, "Failed to create the vCPU thread");
> +
> + /* Spawn a scheduler thread to force-migrate vCPUs to various pCPUs */
> + ret = pthread_create(&pt_sched, NULL, vcpus_migrate_func, &migrate_data);

Why do you want to spawn another thread to run vcpus_migrate_func(),
rather than calling that from the current thread ?

> + TEST_ASSERT(!ret, "Failed to create the scheduler thread for migrating the vCPUs");
> +
> + pthread_join(pt_sched, NULL);
> + pthread_join(pt_vcpu, NULL);
> +
> + destroy_vpmu_vm(vpmu_vm);
> +}
> +
> static void run_tests(uint64_t pmcr_n)
> {
> run_counter_access_tests(pmcr_n);
> run_kvm_event_filter_test();
> run_kvm_evtype_filter_test();
> + run_vcpu_migration_test(pmcr_n);
> }
>
> /*
> @@ -1121,12 +1271,53 @@ static uint64_t get_pmcr_n_limit(void)
> return FIELD_GET(ARMV8_PMU_PMCR_N, pmcr);
> }
>
> -int main(void)
> +static void print_help(char *name)
> +{
> + pr_info("Usage: %s [-h] [-i vcpu_migration_test_iterations] [-m vcpu_migration_freq_ms]\n",
> + name);
> + pr_info("\t-i: Number of iterations of vCPU migrations test (default: %u)\n",
> + VCPU_MIGRATIONS_TEST_ITERS_DEF);
> + pr_info("\t-m: Frequency (in ms) of vCPUs to migrate to different pCPU. (default: %u)\n",
> + VCPU_MIGRATIONS_TEST_MIGRATION_FREQ_MS);
> + pr_info("\t-h: print this help screen\n");
> +}
> +
> +static bool parse_args(int argc, char *argv[])
> +{
> + int opt;
> +
> + while ((opt = getopt(argc, argv, "hi:m:")) != -1) {
> + switch (opt) {
> + case 'i':
> + test_args.vcpu_migration_test_iter =
> + atoi_positive("Nr vCPU migration iterations", optarg);
> + break;
> + case 'm':
> + test_args.vcpu_migration_test_migrate_freq_ms =
> + atoi_positive("vCPU migration frequency", optarg);
> + break;
> + case 'h':
> + default:
> + goto err;
> + }
> + }
> +
> + return true;
> +
> +err:
> + print_help(argv[0]);
> + return false;
> +}
> +
> +int main(int argc, char *argv[])
> {
> uint64_t pmcr_n;
>
> TEST_REQUIRE(kvm_has_cap(KVM_CAP_ARM_PMU_V3));
>
> + if (!parse_args(argc, argv))
> + exit(KSFT_SKIP);
> +
> pmcr_n = get_pmcr_n_limit();
> run_tests(pmcr_n);
>
> --
> 2.39.1.581.gbfd45094c4-goog
>

Thanks,
Reiji