On Fri, Jun 11, 2021 at 4:57 PM David Matlack <dmatlack@xxxxxxxxxx> wrote:
>
> This test measures the performance effects of KVM's access tracking.
> Access tracking is driven by the MMU notifiers test_young, clear_young,
> and clear_flush_young. These notifiers do not have a direct userspace
> API, however the clear_young notifier can be triggered by marking a
> pages as idle in /sys/kernel/mm/page_idle/bitmap. This test leverages
> that mechanism to enable access tracking on guest memory.
>
> To measure performance this test runs a VM with a configurable number of
> vCPUs that each touch every page in disjoint regions of memory.
> Performance is measured in the time it takes all vCPUs to finish
> touching their predefined region.
>
> Example invocation:
>
> $ ./access_tracking_perf_test -v 8
> Testing guest mode: PA-bits:ANY, VA-bits:48, 4K pages
> guest physical test memory offset: 0xffdfffff000
>
> Populating memory : 1.337752570s
> Writing to populated memory : 0.010177640s
> Reading from populated memory : 0.009548239s
> Mark memory idle : 23.973131748s
> Writing to idle memory : 0.063584496s
> Mark memory idle : 24.924652964s
> Reading from idle memory : 0.062042814s
>
> Breaking down the results:
>
> * "Populating memory": The time it takes for all vCPUs to perform the
> first write to every page in their region.
>
> * "Writing to populated memory" / "Reading from populated memory": The
> time it takes for all vCPUs to write and read to every page in their
> region after it has been populated. This serves as a control for the
> later results.
>
> * "Mark memory idle": The time it takes for every vCPU to mark every
> page in their region as idle through page_idle.
>
> * "Writing to idle memory" / "Reading from idle memory": The time it
> takes for all vCPUs to write and read to every page in their region
> after it has been marked idle.
>
> This test should be portable across architectures but it is only enabled
> for x86_64 since that's all I have tested.
>
> Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
> tools/testing/selftests/kvm/.gitignore | 1 +
> tools/testing/selftests/kvm/Makefile | 1 +
> .../selftests/kvm/access_tracking_perf_test.c | 419 ++++++++++++++++++
> 3 files changed, 421 insertions(+)
> create mode 100644 tools/testing/selftests/kvm/access_tracking_perf_test.c
>
> diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
> index bd83158e0e0b..32a362d71e05 100644
> --- a/tools/testing/selftests/kvm/.gitignore
> +++ b/tools/testing/selftests/kvm/.gitignore
> @@ -34,6 +34,7 @@
> /x86_64/xen_vmcall_test
> /x86_64/xss_msr_test
> /x86_64/vmx_pmu_msrs_test
> +/access_tracking_perf_test
> /demand_paging_test
> /dirty_log_test
> /dirty_log_perf_test
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index e439d027939d..9f1b478da92b 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -67,6 +67,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/tsc_msrs_test
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_pmu_msrs_test
> TEST_GEN_PROGS_x86_64 += x86_64/xen_shinfo_test
> TEST_GEN_PROGS_x86_64 += x86_64/xen_vmcall_test
> +TEST_GEN_PROGS_x86_64 += access_tracking_perf_test
> TEST_GEN_PROGS_x86_64 += demand_paging_test
> TEST_GEN_PROGS_x86_64 += dirty_log_test
> TEST_GEN_PROGS_x86_64 += dirty_log_perf_test
> diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> new file mode 100644
> index 000000000000..60828f2d780f
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> @@ -0,0 +1,419 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * access_tracking_test
> + *
> + * Copyright (C) 2021, Google, Inc.
> + *
> + * This test measures the performance effects of KVM's access tracking.
> + * Access tracking is driven by the MMU notifiers test_young, clear_young, and
> + * clear_flush_young. These notifiers do not have a direct userspace API,
> + * however the clear_young notifier can be triggered by marking a pages as idle
> + * in /sys/kernel/mm/page_idle/bitmap. This test leverages that mechanism to
> + * enable access tracking on guest memory.
> + *
> + * To measure performance this test runs a VM with a configurable number of
> + * vCPUs that each touch every page in disjoint regions of memory. Performance
> + * is measured in the time it takes all vCPUs to finish touching their
> + * predefined region.
> + *
> + * Note that a deterministic correctness test of access tracking is not possible
> + * by using page_idle as it exists today. This is for a few reasons:
> + *
> + * 1. page_idle only issues clear_young notifiers, which lack a TLB flush. This
> + * means subsequent guest accesses are not guaranteed to see page table
> + * updates made by KVM until some time in the future.
> + *
> + * 2. page_idle only operates on LRU pages. Newly allocated pages are not
> + * immediately allocated to LRU lists. Instead they are held in a "pagevec",
> + * which is drained to LRU lists some time in the future. There is no
> + * userspace API to force this drain to occur.
> + *
> + * These limitations are worked around in this test by using a large enough
> + * region of memory for each vCPU such that the number of translations cached in
> + * the TLB and the number of pages held in pagevecs are a small fraction of the
> + * overall workload. And if either of those conditions are not true this test
> + * will fail rather than silently passing.
> + */
> +#include <inttypes.h>
> +#include <limits.h>
> +#include <pthread.h>
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +
> +#include "kvm_util.h"
> +#include "test_util.h"
> +#include "perf_test_util.h"
> +#include "guest_modes.h"
> +
> +/* Global variable used to synchronize all of the vCPU threads. */
> +static int iteration = -1;
> +
> +/* Defines what vCPU threads should do during a given iteration. */
> +static enum {
> + /* Run the vCPU to access all its memory. */
> + ITERATION_ACCESS_MEMORY,
> + /* Mark the vCPU's memory idle in page_idle. */
> + 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];
> +
> +/* Whether to overlap the regions of memory vCPUs access. */
> +static bool overlap_memory_access;
> +
> +struct test_params {
> + /* The backing source for the region of memory. */
> + enum vm_mem_backing_src_type backing_src;
> +
> + /* The amount of memory to allocate for each vCPU. */
> + uint64_t vcpu_memory_bytes;
> +
> + /* The number of vCPUs to create in the VM. */
> + int vcpus;
> +};
> +
> +static uint64_t pread_uint64(int fd, const char *filename, uint64_t index)
> +{
> + uint64_t value;
> + off_t offset = index * sizeof(value);
> +
> + TEST_ASSERT(pread(fd, &value, sizeof(value), offset) == sizeof(value),
> + "pread from %s offset 0x%" PRIx64 " failed!",
> + filename, offset);
> +
> + return value;
> +
> +}
> +
> +static uint64_t lookup_pfn(int pagemap_fd, struct kvm_vm *vm, uint64_t gva)
> +{
> + uint64_t hva = (uint64_t) addr_gva2hva(vm, gva);
> + uint64_t entry;
> +
> + entry = pread_uint64(pagemap_fd, "pagemap", hva / getpagesize());
> + if (!(entry & (1ULL << 63)))
> + return 0;
> +
> + return (entry & ((1ULL << 55) - 1));
It might be helpful to document these shifts and other constants in this test.
> +}
> +
> +static bool is_page_idle(int page_idle_fd, uint64_t pfn)
> +{
> + uint64_t bits = pread_uint64(page_idle_fd, "page_idle", pfn / 64);
> +
> + return !!((bits >> (pfn % 64)) & 1);
> +}
> +
> +static void mark_page_idle(int page_idle_fd, uint64_t pfn)
> +{
> + uint64_t bits = 1ULL << (pfn % 64);
> +
> + TEST_ASSERT(pwrite(page_idle_fd, &bits, 8, 8 * (pfn / 64)) == 8,
> + "Set page_idle bits for PFN 0x%" PRIx64, pfn);
> +}
> +
> +static void mark_vcpu_memory_idle(struct kvm_vm *vm, int vcpu_id)
> +{
> + uint64_t base_gva = perf_test_args.vcpu_args[vcpu_id].gva;
> + uint64_t pages = perf_test_args.vcpu_args[vcpu_id].pages;
> + uint64_t page;
> + uint64_t still_idle = 0;
> + uint64_t no_pfn = 0;
> + int page_idle_fd;
> + int pagemap_fd;
> +
> + /* If vCPUs are using an overlapping region, let vCPU 0 mark it idle. */
> + if (overlap_memory_access && vcpu_id)
> + return;
> +
> + page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
> + TEST_ASSERT(page_idle_fd > 0, "Failed to open page_idle.");
> +
> + pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
> + TEST_ASSERT(pagemap_fd > 0, "Failed to open pagemap.");
Should this have an early skip-check too? I assume not all users of
this test will be running with the privileges required to access
pagemap.
> +
> + for (page = 0; page < pages; page++) {
> + uint64_t gva = base_gva + page * perf_test_args.guest_page_size;
> + uint64_t pfn = lookup_pfn(pagemap_fd, vm, gva);
> +
> + if (!pfn) {
> + no_pfn++;
> + continue;
> + }
> +
> + if (is_page_idle(page_idle_fd, pfn)) {
> + still_idle++;
> + continue;
> + }
> +
> + mark_page_idle(page_idle_fd, pfn);
> + }
> +
> + /*
> + * Assumption: Less than 1% of pages are going to be swapped out from
> + * under us during this test.
> + */
> + TEST_ASSERT(no_pfn < pages / 100,
> + "vCPU %d: No PFN for %" PRIu64 " out of %" PRIu64 " pages.",
> + vcpu_id, no_pfn, pages);
> +
> + /*
> + * Test that at least 90% of memory has been marked idle (the rest might
> + * not be marked idle because the pages have not yet made it to an LRU
> + * list or the translations are still cached in the TLB). 90% is
> + * arbitrary; high enough that we ensure most memory access went through
> + * access tracking but low enough as to not make the test too brittle
> + * over time and across architectures.
> + */
> + TEST_ASSERT(still_idle < pages / 10,
> + "vCPU%d: Too many pages still idle (%"PRIu64 " out of %"
> + PRIu64 ").\n",
> + vcpu_id, still_idle, pages);
> +
> + close(page_idle_fd);
> + close(pagemap_fd);
> +}
> +
> +static void assert_ucall(struct kvm_vm *vm, uint32_t vcpu_id,
> + uint64_t expected_ucall)
> +{
> + struct ucall uc;
> + uint64_t actual_ucall = get_ucall(vm, vcpu_id, &uc);
> +
> + TEST_ASSERT(expected_ucall == actual_ucall,
> + "Guest exited unexpectedly (expected ucall %" PRIu64
> + ", got %" PRIu64 ")",
> + 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(void *arg)
> +{
> + struct perf_test_vcpu_args *vcpu_args = arg;
> + struct kvm_vm *vm = perf_test_args.vm;
> + int vcpu_id = vcpu_args->vcpu_id;
> + int current_iteration = -1;
> +
> + vcpu_args_set(vm, vcpu_id, 1, vcpu_id);
> +
> + while (spin_wait_for_next_iteration(¤t_iteration)) {
> + switch (READ_ONCE(iteration_work)) {
> + case ITERATION_ACCESS_MEMORY:
> + vcpu_run(vm, vcpu_id);
> + assert_ucall(vm, vcpu_id, UCALL_SYNC);
> + break;
> + case ITERATION_MARK_IDLE:
> + mark_vcpu_memory_idle(vm, vcpu_id);
> + break;
> + };
> +
> + vcpu_last_completed_iteration[vcpu_id] = current_iteration;
> + }
> +
> + return NULL;
> +}
> +
> +static void spin_wait_for_vcpu(int vcpu_id, int target_iteration)
> +{
> + while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id]) !=
> + target_iteration) {
> + continue;
> + }
> +}
> +
> +/* The type of memory accesses to perform in the VM. */
> +enum access_type {
> + ACCESS_READ,
> + ACCESS_WRITE,
> +};
> +
> +static void run_iteration(struct kvm_vm *vm, int vcpus, const char *description)
> +{
> + struct timespec ts_start;
> + struct timespec ts_elapsed;
> + int next_iteration;
> + int vcpu_id;
> +
> + /* Kick off the vCPUs by incrementing iteration. */
> + next_iteration = ++iteration;
> +
> + clock_gettime(CLOCK_MONOTONIC, &ts_start);
> +
> + /* Wait for all vCPUs to finish the iteration. */
> + for (vcpu_id = 0; vcpu_id < vcpus; vcpu_id++)
> + spin_wait_for_vcpu(vcpu_id, next_iteration);
> +
> + ts_elapsed = timespec_elapsed(ts_start);
> + pr_info("%-30s: %ld.%09lds\n",
> + description, ts_elapsed.tv_sec, ts_elapsed.tv_nsec);
> +}
> +
> +static void access_memory(struct kvm_vm *vm, int vcpus, enum access_type access,
> + const char *description)
> +{
> + perf_test_args.wr_fract = (access == ACCESS_READ) ? INT_MAX : 1;
> + sync_global_to_guest(vm, perf_test_args);
> + iteration_work = ITERATION_ACCESS_MEMORY;
> + run_iteration(vm, vcpus, description);
> +}
> +
> +static void mark_memory_idle(struct kvm_vm *vm, int vcpus)
> +{
> + /*
> + * Even though this parallelizes the work across vCPUs, this is still a
> + * very slow operation because page_idle forces the test to mark one pfn
> + * at a time and the clear_young notifier serializes on the KVM MMU
> + * lock.
> + */
> + pr_debug("Marking VM memory idle (slow)...\n");
> + iteration_work = ITERATION_MARK_IDLE;
> + run_iteration(vm, vcpus, "Mark memory idle");
> +}
> +
> +static pthread_t *create_vcpu_threads(int vcpus)
> +{
> + pthread_t *vcpu_threads;
> + int i;
> +
> + vcpu_threads = malloc(vcpus * sizeof(vcpu_threads[0]));
> + TEST_ASSERT(vcpu_threads, "Failed to allocate vcpu_threads.");
> +
> + for (i = 0; i < vcpus; i++) {
> + vcpu_last_completed_iteration[i] = iteration;
> + pthread_create(&vcpu_threads[i], NULL, vcpu_thread_main,
> + &perf_test_args.vcpu_args[i]);
> + }
> +
> + return vcpu_threads;
> +}
> +
> +static void terminate_vcpu_threads(pthread_t *vcpu_threads, int vcpus)
> +{
> + int i;
> +
> + /* Set done to signal the vCPU threads to exit */
> + done = true;
> +
> + for (i = 0; i < vcpus; i++)
> + pthread_join(vcpu_threads[i], NULL);
> +}
> +
> +static void run_test(enum vm_guest_mode mode, void *arg)
> +{
> + struct test_params *params = arg;
> + struct kvm_vm *vm;
> + pthread_t *vcpu_threads;
> + int vcpus = params->vcpus;
> +
> + vm = perf_test_create_vm(mode, vcpus, params->vcpu_memory_bytes,
> + params->backing_src);
> +
> + perf_test_setup_vcpus(vm, vcpus, params->vcpu_memory_bytes,
> + !overlap_memory_access);
> +
> + vcpu_threads = create_vcpu_threads(vcpus);
> +
> + pr_info("\n");
> + access_memory(vm, vcpus, ACCESS_WRITE, "Populating memory");
> +
> + /* As a control, read and write to the populated memory first. */
> + access_memory(vm, vcpus, ACCESS_WRITE, "Writing to populated memory");
> + access_memory(vm, vcpus, ACCESS_READ, "Reading from populated memory");
> +
> + /* Repeat on memory that has been marked as idle. */
> + mark_memory_idle(vm, vcpus);
> + access_memory(vm, vcpus, ACCESS_WRITE, "Writing to idle memory");
> + mark_memory_idle(vm, vcpus);
> + access_memory(vm, vcpus, ACCESS_READ, "Reading from idle memory");
> +
> + terminate_vcpu_threads(vcpu_threads, vcpus);
> + free(vcpu_threads);
> + perf_test_destroy_vm(vm);
> +}
> +
> +static void help(char *name)
> +{
> + puts("");
> + printf("usage: %s [-h] [-m mode] [-b vcpu_bytes] [-v vcpus] [-o] [-s mem_type]\n",
> + name);
> + puts("");
> + printf(" -h: Display this help message.");
> + guest_modes_help();
> + printf(" -b: specify the size of the memory region which should be\n"
> + " dirtied by each vCPU. e.g. 10M or 3G.\n"
> + " (default: 1G)\n");
> + printf(" -v: specify the number of vCPUs to run.\n");
> + printf(" -o: Overlap guest memory accesses instead of partitioning\n"
> + " them into a separate region of memory for each vCPU.\n");
> + printf(" -s: specify the type of memory that should be used to\n"
> + " back the guest data region.\n\n");
> + backing_src_help();
> + puts("");
> + exit(0);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + struct test_params params = {
> + .backing_src = VM_MEM_SRC_ANONYMOUS,
> + .vcpu_memory_bytes = DEFAULT_PER_VCPU_MEM_SIZE,
> + .vcpus = 1,
> + };
> + int page_idle_fd;
> + int opt;
> +
> + guest_modes_append_default();
> +
> + while ((opt = getopt(argc, argv, "hm:b:v:os:")) != -1) {
> + switch (opt) {
> + case 'm':
> + guest_modes_cmdline(optarg);
> + break;
> + case 'b':
> + params.vcpu_memory_bytes = parse_size(optarg);
> + break;
> + case 'v':
> + params.vcpus = atoi(optarg);
> + break;
> + case 'o':
> + overlap_memory_access = true;
> + break;
> + case 's':
> + params.backing_src = parse_backing_src_type(optarg);
> + break;
> + case 'h':
> + default:
> + help(argv[0]);
> + break;
> + }
> + }
> +
> + page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
> + if (page_idle_fd < 0) {
> + print_skip("CONFIG_IDLE_PAGE_TRACKING is not enabled");
> + exit(KSFT_SKIP);
> + }
> + close(page_idle_fd);
> +
> + for_each_guest_mode(run_test, ¶ms);
> +
> + return 0;
> +}
> --
> 2.32.0.272.g935e593368-goog
>
