Re: [PATCH v3 6/8] KVM: selftests: Support multiple vCPUs in demand paging test
From: Andrew Jones
Date: Tue Jan 07 2020 - 10:28:06 EST
On Mon, Dec 16, 2019 at 01:38:59PM -0800, Ben Gardon wrote:
> Most VMs have multiple vCPUs, the concurrent execution of which has a
> substantial impact on demand paging performance. Add an option to create
> multiple vCPUs to each access disjoint regions of memory.
>
> Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
> .../selftests/kvm/demand_paging_test.c | 199 ++++++++++++------
> 1 file changed, 136 insertions(+), 63 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> index 8ede26e088ab6..2b80f614dd537 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -24,8 +24,6 @@
> #include "kvm_util.h"
> #include "processor.h"
>
> -#define VCPU_ID 1
> -
> /* The memory slot index demand page */
> #define TEST_MEM_SLOT_INDEX 1
>
> @@ -34,6 +32,12 @@
>
> #define DEFAULT_GUEST_TEST_MEM_SIZE (1 << 30) /* 1G */
>
> +#ifdef PRINT_PER_VCPU_UPDATES
> +#define PER_VCPU_DEBUG(...) DEBUG(__VA_ARGS__)
> +#else
> +#define PER_VCPU_DEBUG(...)
> +#endif
> +
> /*
> * Guest/Host shared variables. Ensure addr_gva2hva() and/or
> * sync_global_to/from_guest() are used when accessing from
> @@ -76,10 +80,6 @@ static void guest_code(uint64_t gva, uint64_t pages)
> GUEST_SYNC(1);
> }
>
> -/* Points to the test VM memory region on which we are doing demand paging */
> -static void *host_test_mem;
> -static uint64_t host_num_pages;
> -
> struct vcpu_thread_args {
> uint64_t gva;
> uint64_t pages;
> @@ -113,18 +113,32 @@ static void *vcpu_worker(void *data)
> return NULL;
> }
>
> -static struct kvm_vm *create_vm(enum vm_guest_mode mode, uint32_t vcpuid,
> - uint64_t extra_mem_pages, void *guest_code)
> +#define PAGE_SHIFT_4K 12
> +#define PTES_PER_PT 512
> +
> +static struct kvm_vm *create_vm(enum vm_guest_mode mode, int vcpus,
> + uint64_t vcpu_wss)
> {
> struct kvm_vm *vm;
> - uint64_t extra_pg_pages = extra_mem_pages / 512 * 2;
> + uint64_t pages = DEFAULT_GUEST_PHY_PAGES;
>
> - vm = _vm_create(mode, DEFAULT_GUEST_PHY_PAGES + extra_pg_pages, O_RDWR);
> + /* Account for a few pages per-vCPU for stacks */
> + pages += DEFAULT_STACK_PGS * vcpus;
> +
> + /*
> + * Reserve twice the ammount of memory needed to map the test region and
> + * the page table / stacks region, at 4k, for page tables. Do the
> + * calculation with 4K page size: the smallest of all archs. (e.g., 64K
> + * page size guest will need even less memory for page tables).
> + */
> + pages += (2 * pages) / PTES_PER_PT;
> + pages += ((2 * vcpus * vcpu_wss) >> PAGE_SHIFT_4K) / PTES_PER_PT;
> +
> + vm = _vm_create(mode, pages, O_RDWR);
> kvm_vm_elf_load(vm, program_invocation_name, 0, 0);
> #ifdef __x86_64__
> vm_create_irqchip(vm);
> #endif
> - vm_vcpu_add_default(vm, vcpuid, guest_code);
> return vm;
> }
>
> @@ -232,15 +246,13 @@ static void *uffd_handler_thread_fn(void *arg)
>
> static int setup_demand_paging(struct kvm_vm *vm,
> pthread_t *uffd_handler_thread,
> - useconds_t uffd_delay)
> + useconds_t uffd_delay,
> + struct uffd_handler_args *uffd_args,
> + void *hva, uint64_t len)
> {
> int uffd;
> struct uffdio_api uffdio_api;
> struct uffdio_register uffdio_register;
> - struct uffd_handler_args uffd_args;
> -
> - guest_data_prototype = malloc(host_page_size);
> - memset(guest_data_prototype, 0xAB, host_page_size);
>
> uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
> if (uffd == -1) {
> @@ -255,8 +267,8 @@ static int setup_demand_paging(struct kvm_vm *vm,
> return -1;
> }
>
> - uffdio_register.range.start = (uint64_t)host_test_mem;
> - uffdio_register.range.len = host_num_pages * host_page_size;
> + uffdio_register.range.start = (uint64_t)hva;
> + uffdio_register.range.len = len;
> uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
> if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1) {
> DEBUG("ioctl uffdio_register failed\n");
> @@ -269,42 +281,37 @@ static int setup_demand_paging(struct kvm_vm *vm,
> return -1;
> }
>
> - uffd_args.uffd = uffd;
> - uffd_args.delay = uffd_delay;
> + uffd_args->uffd = uffd;
> + uffd_args->delay = uffd_delay;
> pthread_create(uffd_handler_thread, NULL, uffd_handler_thread_fn,
> - &uffd_args);
> + uffd_args);
> +
> + PER_VCPU_DEBUG("Created uffd thread for HVA range [%p, %p)\n",
> + hva, hva + len);
>
> return 0;
> }
>
> -#define PAGE_SHIFT_4K 12
> -
> static void run_test(enum vm_guest_mode mode, bool use_uffd,
> - useconds_t uffd_delay, uint64_t vcpu_wss)
> + useconds_t uffd_delay, int vcpus, uint64_t vcpu_wss)
> {
> - pthread_t vcpu_thread;
> - pthread_t uffd_handler_thread;
> + pthread_t *vcpu_threads;
> + pthread_t *uffd_handler_threads = NULL;
> + struct uffd_handler_args *uffd_args = NULL;
> struct kvm_vm *vm;
> - struct vcpu_thread_args vcpu_args;
> + struct vcpu_thread_args *vcpu_args;
> uint64_t guest_num_pages;
> + int vcpu_id;
> int r;
>
> - /*
> - * We reserve page table for twice the ammount of memory we intend
> - * to use in the test region for demand paging. Here we do the
> - * calculation with 4K page size which is the smallest so the page
> - * number will be enough for all archs. (e.g., 64K page size guest
> - * will need even less memory for page tables).
> - */
> - vm = create_vm(mode, VCPU_ID, (2 * vcpu_wss) >> PAGE_SHIFT_4K,
> - guest_code);
> + vm = create_vm(mode, vcpus, vcpu_wss);
>
> guest_page_size = vm_get_page_size(vm);
>
> TEST_ASSERT(vcpu_wss % guest_page_size == 0,
> "Guest memory size is not guest page size aligned.");
>
> - guest_num_pages = vcpu_wss / guest_page_size;
> + guest_num_pages = (vcpus * vcpu_wss) / guest_page_size;
>
> #ifdef __s390x__
> /* Round up to multiple of 1M (segment size) */
> @@ -316,13 +323,12 @@ static void run_test(enum vm_guest_mode mode, bool use_uffd,
> */
> TEST_ASSERT(guest_num_pages < vm_get_max_gfn(vm),
> "Requested more guest memory than address space allows.\n"
> - " guest pages: %lx max gfn: %lx\n",
> - guest_num_pages, vm_get_max_gfn(vm));
> + " guest pages: %lx max gfn: %lx vcpus: %d wss: %lx]\n",
> + guest_num_pages, vm_get_max_gfn(vm), vcpus, vcpu_wss);
>
> host_page_size = getpagesize();
> TEST_ASSERT(vcpu_wss % host_page_size == 0,
> "Guest memory size is not host page size aligned.");
> - host_num_pages = vcpu_wss / host_page_size;
>
> guest_test_phys_mem = (vm_get_max_gfn(vm) - guest_num_pages) *
> guest_page_size;
> @@ -347,43 +353,102 @@ static void run_test(enum vm_guest_mode mode, bool use_uffd,
> virt_map(vm, guest_test_virt_mem, guest_test_phys_mem,
> guest_num_pages * guest_page_size, 0);
>
> - /* Cache the HVA pointer of the region */
> - host_test_mem = addr_gpa2hva(vm, (vm_paddr_t)guest_test_phys_mem);
> + /* Export the shared variables to the guest */
> + sync_global_to_guest(vm, host_page_size);
> + sync_global_to_guest(vm, guest_page_size);
> +
> + guest_data_prototype = malloc(host_page_size);
> + TEST_ASSERT(guest_data_prototype, "Memory allocation failed");
> + memset(guest_data_prototype, 0xAB, host_page_size);
> +
> + vcpu_threads = malloc(vcpus * sizeof(*vcpu_threads));
> + TEST_ASSERT(vcpu_threads, "Memory allocation failed");
>
> if (use_uffd) {
> - /* Set up user fault fd to handle demand paging requests. */
> quit_uffd_thread = false;
> - r = setup_demand_paging(vm, &uffd_handler_thread,
> - uffd_delay);
> - if (r < 0)
> - exit(-r);
> +
> + uffd_handler_threads =
> + malloc(vcpus * sizeof(*uffd_handler_threads));
> + TEST_ASSERT(uffd_handler_threads, "Memory allocation failed");
> +
> + uffd_args = malloc(vcpus * sizeof(*uffd_args));
> + TEST_ASSERT(uffd_args, "Memory allocation failed");
> }
>
> + vcpu_args = malloc(vcpus * sizeof(*vcpu_args));
> + TEST_ASSERT(vcpu_args, "Memory allocation failed");
> +
> + for (vcpu_id = 0; vcpu_id < vcpus; vcpu_id++) {
> + vm_paddr_t vcpu_gpa;
> + void *vcpu_hva;
> +
> + vm_vcpu_add_default(vm, vcpu_id, guest_code);
> +
> + vcpu_gpa = guest_test_phys_mem + (vcpu_id * vcpu_wss);
> + PER_VCPU_DEBUG("Added VCPU %d with test mem gpa [%lx, %lx)\n",
> + vcpu_id, vcpu_gpa, vcpu_gpa + vcpu_wss);
> +
> + /* Cache the HVA pointer of the region */
> + vcpu_hva = addr_gpa2hva(vm, vcpu_gpa);
> +
> + if (use_uffd) {
> + /*
> + * Set up user fault fd to handle demand paging
> + * requests.
> + */
> + r = setup_demand_paging(vm,
> + &uffd_handler_threads[vcpu_id],
> + uffd_delay, &uffd_args[vcpu_id],
> + vcpu_hva, vcpu_wss);
> + if (r < 0)
> + exit(-r);
> + }
> +
> #ifdef __x86_64__
> - vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
> + vcpu_set_cpuid(vm, vcpu_id, kvm_get_supported_cpuid());
> #endif
>
> - /* Export the shared variables to the guest */
> - sync_global_to_guest(vm, host_page_size);
> - sync_global_to_guest(vm, guest_page_size);
> + vcpu_args[vcpu_id].vm = vm;
> + vcpu_args[vcpu_id].vcpu_id = vcpu_id;
> + vcpu_args[vcpu_id].gva = guest_test_virt_mem +
> + (vcpu_id * vcpu_wss);
> + vcpu_args[vcpu_id].pages = vcpu_wss / guest_page_size;
> + }
> +
> + DEBUG("Finished creating vCPUs and starting uffd threads\n");
> +
> + for (vcpu_id = 0; vcpu_id < vcpus; vcpu_id++) {
> + pthread_create(&vcpu_threads[vcpu_id], NULL, vcpu_worker,
> + &vcpu_args[vcpu_id]);
> + }
> +
> + DEBUG("Started all vCPUs\n");
>
> - vcpu_args.vm = vm;
> - vcpu_args.vcpu_id = VCPU_ID;
> - vcpu_args.gva = guest_test_virt_mem;
> - vcpu_args.pages = guest_num_pages;
> - pthread_create(&vcpu_thread, NULL, vcpu_worker, &vcpu_args);
> + /* Wait for the vcpu threads to quit */
> + for (vcpu_id = 0; vcpu_id < vcpus; vcpu_id++) {
> + pthread_join(vcpu_threads[vcpu_id], NULL);
> + PER_VCPU_DEBUG("Joined thread for vCPU %d\n", vcpu_id);
> + }
>
> - /* Wait for the vcpu thread to quit */
> - pthread_join(vcpu_thread, NULL);
> + DEBUG("All vCPU threads joined\n");
>
> if (use_uffd) {
> - /* Tell the user fault fd handler thread to quit */
> + /* Tell the user fault fd handler threads to quit */
> quit_uffd_thread = true;
> - pthread_join(uffd_handler_thread, NULL);
> + for (vcpu_id = 0; vcpu_id < vcpus; vcpu_id++)
> + pthread_join(uffd_handler_threads[vcpu_id], NULL);
> }
>
> ucall_uninit(vm);
> kvm_vm_free(vm);
> +
> + free(guest_data_prototype);
> + free(vcpu_threads);
> + if (use_uffd) {
> + free(uffd_handler_threads);
> + free(uffd_args);
> + }
> + free(vcpu_args);
> }
>
> struct vm_guest_mode_params {
> @@ -404,7 +469,7 @@ static void help(char *name)
>
> puts("");
> printf("usage: %s [-h] [-m mode] [-u] [-d uffd_delay_usec]\n"
> - " [-b bytes test memory]\n", name);
> + " [-b bytes test memory] [-v vcpus]\n", name);
> printf(" -m: specify the guest mode ID to test\n"
> " (default: test all supported modes)\n"
> " This option may be used multiple times.\n"
> @@ -419,6 +484,7 @@ static void help(char *name)
> " FD handler to simulate demand paging\n"
> " overheads. Ignored without -u.\n");
> printf(" -b: specify the working set size, in bytes for each vCPU.\n");
> + printf(" -v: specify the number of vCPUs to run.\n");
> puts("");
> exit(0);
> }
> @@ -427,6 +493,7 @@ int main(int argc, char *argv[])
> {
> bool mode_selected = false;
> uint64_t vcpu_wss = DEFAULT_GUEST_TEST_MEM_SIZE;
> + int vcpus = 1;
> unsigned int mode;
> int opt, i;
> bool use_uffd = false;
> @@ -439,7 +506,7 @@ int main(int argc, char *argv[])
> vm_guest_mode_params_init(VM_MODE_P40V48_4K, true, true);
> #endif
>
> - while ((opt = getopt(argc, argv, "hm:ud:b:")) != -1) {
> + while ((opt = getopt(argc, argv, "hm:ud:b:v:")) != -1) {
> switch (opt) {
> case 'm':
> if (!mode_selected) {
> @@ -462,6 +529,12 @@ int main(int argc, char *argv[])
> break;
> case 'b':
> vcpu_wss = strtoull(optarg, NULL, 0);
> + break;
There's that missing break. It's good to test each patch to ensure
bisectability.
> + case 'v':
> + vcpus = atoi(optarg);
> + TEST_ASSERT(vcpus > 0,
> + "Must have a positive number of vCPUs");
> + break;
> case 'h':
> default:
> help(argv[0]);
> @@ -475,7 +548,7 @@ int main(int argc, char *argv[])
> TEST_ASSERT(vm_guest_mode_params[i].supported,
> "Guest mode ID %d (%s) not supported.",
> i, vm_guest_mode_string(i));
> - run_test(i, use_uffd, uffd_delay, vcpu_wss);
> + run_test(i, use_uffd, uffd_delay, vcpus, vcpu_wss);
> }
>
> return 0;
> --
> 2.24.1.735.g03f4e72817-goog
>
Thanks,
drew