395 lines
11 KiB
C
395 lines
11 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* access_tracking_perf_test
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*
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* Copyright (C) 2021, Google, Inc.
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*
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* This test measures the performance effects of KVM's access tracking.
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* Access tracking is driven by the MMU notifiers test_young, clear_young, and
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* clear_flush_young. These notifiers do not have a direct userspace API,
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* however the clear_young notifier can be triggered by marking a pages as idle
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* in /sys/kernel/mm/page_idle/bitmap. This test leverages that mechanism to
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* enable access tracking on guest memory.
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*
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* To measure performance this test runs a VM with a configurable number of
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* vCPUs that each touch every page in disjoint regions of memory. Performance
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* is measured in the time it takes all vCPUs to finish touching their
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* predefined region.
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*
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* Note that a deterministic correctness test of access tracking is not possible
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* by using page_idle as it exists today. This is for a few reasons:
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*
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* 1. page_idle only issues clear_young notifiers, which lack a TLB flush. This
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* means subsequent guest accesses are not guaranteed to see page table
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* updates made by KVM until some time in the future.
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*
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* 2. page_idle only operates on LRU pages. Newly allocated pages are not
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* immediately allocated to LRU lists. Instead they are held in a "pagevec",
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* which is drained to LRU lists some time in the future. There is no
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* userspace API to force this drain to occur.
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*
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* These limitations are worked around in this test by using a large enough
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* region of memory for each vCPU such that the number of translations cached in
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* the TLB and the number of pages held in pagevecs are a small fraction of the
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* overall workload. And if either of those conditions are not true (for example
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* in nesting, where TLB size is unlimited) this test will print a warning
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* rather than silently passing.
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*/
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#include <inttypes.h>
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#include <limits.h>
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#include <pthread.h>
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#include <sys/mman.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include "kvm_util.h"
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#include "test_util.h"
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#include "perf_test_util.h"
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#include "guest_modes.h"
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/* Global variable used to synchronize all of the vCPU threads. */
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static int iteration;
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/* Defines what vCPU threads should do during a given iteration. */
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static enum {
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/* Run the vCPU to access all its memory. */
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ITERATION_ACCESS_MEMORY,
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/* Mark the vCPU's memory idle in page_idle. */
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ITERATION_MARK_IDLE,
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} iteration_work;
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/* Set to true when vCPU threads should exit. */
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static bool done;
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/* The iteration that was last completed by each vCPU. */
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static int vcpu_last_completed_iteration[KVM_MAX_VCPUS];
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/* Whether to overlap the regions of memory vCPUs access. */
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static bool overlap_memory_access;
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struct test_params {
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/* The backing source for the region of memory. */
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enum vm_mem_backing_src_type backing_src;
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/* The amount of memory to allocate for each vCPU. */
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uint64_t vcpu_memory_bytes;
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/* The number of vCPUs to create in the VM. */
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int nr_vcpus;
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};
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static uint64_t pread_uint64(int fd, const char *filename, uint64_t index)
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{
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uint64_t value;
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off_t offset = index * sizeof(value);
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TEST_ASSERT(pread(fd, &value, sizeof(value), offset) == sizeof(value),
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"pread from %s offset 0x%" PRIx64 " failed!",
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filename, offset);
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return value;
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}
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#define PAGEMAP_PRESENT (1ULL << 63)
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#define PAGEMAP_PFN_MASK ((1ULL << 55) - 1)
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static uint64_t lookup_pfn(int pagemap_fd, struct kvm_vm *vm, uint64_t gva)
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{
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uint64_t hva = (uint64_t) addr_gva2hva(vm, gva);
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uint64_t entry;
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uint64_t pfn;
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entry = pread_uint64(pagemap_fd, "pagemap", hva / getpagesize());
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if (!(entry & PAGEMAP_PRESENT))
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return 0;
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pfn = entry & PAGEMAP_PFN_MASK;
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__TEST_REQUIRE(pfn, "Looking up PFNs requires CAP_SYS_ADMIN");
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return pfn;
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}
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static bool is_page_idle(int page_idle_fd, uint64_t pfn)
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{
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uint64_t bits = pread_uint64(page_idle_fd, "page_idle", pfn / 64);
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return !!((bits >> (pfn % 64)) & 1);
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}
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static void mark_page_idle(int page_idle_fd, uint64_t pfn)
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{
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uint64_t bits = 1ULL << (pfn % 64);
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TEST_ASSERT(pwrite(page_idle_fd, &bits, 8, 8 * (pfn / 64)) == 8,
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"Set page_idle bits for PFN 0x%" PRIx64, pfn);
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}
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static void mark_vcpu_memory_idle(struct kvm_vm *vm,
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struct perf_test_vcpu_args *vcpu_args)
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{
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int vcpu_idx = vcpu_args->vcpu_idx;
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uint64_t base_gva = vcpu_args->gva;
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uint64_t pages = vcpu_args->pages;
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uint64_t page;
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uint64_t still_idle = 0;
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uint64_t no_pfn = 0;
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int page_idle_fd;
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int pagemap_fd;
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/* If vCPUs are using an overlapping region, let vCPU 0 mark it idle. */
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if (overlap_memory_access && vcpu_idx)
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return;
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page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
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TEST_ASSERT(page_idle_fd > 0, "Failed to open page_idle.");
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pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
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TEST_ASSERT(pagemap_fd > 0, "Failed to open pagemap.");
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for (page = 0; page < pages; page++) {
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uint64_t gva = base_gva + page * perf_test_args.guest_page_size;
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uint64_t pfn = lookup_pfn(pagemap_fd, vm, gva);
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if (!pfn) {
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no_pfn++;
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continue;
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}
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if (is_page_idle(page_idle_fd, pfn)) {
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still_idle++;
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continue;
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}
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mark_page_idle(page_idle_fd, pfn);
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}
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/*
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* Assumption: Less than 1% of pages are going to be swapped out from
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* under us during this test.
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*/
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TEST_ASSERT(no_pfn < pages / 100,
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"vCPU %d: No PFN for %" PRIu64 " out of %" PRIu64 " pages.",
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vcpu_idx, no_pfn, pages);
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/*
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* Check that at least 90% of memory has been marked idle (the rest
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* might not be marked idle because the pages have not yet made it to an
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* LRU list or the translations are still cached in the TLB). 90% is
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* arbitrary; high enough that we ensure most memory access went through
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* access tracking but low enough as to not make the test too brittle
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* over time and across architectures.
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*
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* Note that when run in nested virtualization, this check will trigger
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* much more frequently because TLB size is unlimited and since no flush
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* happens, much more pages are cached there and guest won't see the
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* "idle" bit cleared.
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*/
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if (still_idle < pages / 10)
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printf("WARNING: vCPU%d: Too many pages still idle (%" PRIu64
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"out of %" PRIu64 "), this will affect performance results"
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".\n",
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vcpu_idx, still_idle, pages);
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close(page_idle_fd);
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close(pagemap_fd);
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}
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static void assert_ucall(struct kvm_vcpu *vcpu, uint64_t expected_ucall)
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{
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struct ucall uc;
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uint64_t actual_ucall = get_ucall(vcpu, &uc);
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TEST_ASSERT(expected_ucall == actual_ucall,
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"Guest exited unexpectedly (expected ucall %" PRIu64
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", got %" PRIu64 ")",
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expected_ucall, actual_ucall);
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}
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static bool spin_wait_for_next_iteration(int *current_iteration)
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{
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int last_iteration = *current_iteration;
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do {
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if (READ_ONCE(done))
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return false;
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*current_iteration = READ_ONCE(iteration);
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} while (last_iteration == *current_iteration);
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return true;
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}
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static void vcpu_thread_main(struct perf_test_vcpu_args *vcpu_args)
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{
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struct kvm_vcpu *vcpu = vcpu_args->vcpu;
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struct kvm_vm *vm = perf_test_args.vm;
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int vcpu_idx = vcpu_args->vcpu_idx;
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int current_iteration = 0;
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while (spin_wait_for_next_iteration(¤t_iteration)) {
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switch (READ_ONCE(iteration_work)) {
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case ITERATION_ACCESS_MEMORY:
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vcpu_run(vcpu);
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assert_ucall(vcpu, UCALL_SYNC);
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break;
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case ITERATION_MARK_IDLE:
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mark_vcpu_memory_idle(vm, vcpu_args);
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break;
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};
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vcpu_last_completed_iteration[vcpu_idx] = current_iteration;
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}
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}
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static void spin_wait_for_vcpu(int vcpu_idx, int target_iteration)
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{
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while (READ_ONCE(vcpu_last_completed_iteration[vcpu_idx]) !=
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target_iteration) {
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continue;
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}
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}
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/* The type of memory accesses to perform in the VM. */
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enum access_type {
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ACCESS_READ,
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ACCESS_WRITE,
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};
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static void run_iteration(struct kvm_vm *vm, int nr_vcpus, const char *description)
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{
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struct timespec ts_start;
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struct timespec ts_elapsed;
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int next_iteration, i;
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/* Kick off the vCPUs by incrementing iteration. */
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next_iteration = ++iteration;
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clock_gettime(CLOCK_MONOTONIC, &ts_start);
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/* Wait for all vCPUs to finish the iteration. */
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for (i = 0; i < nr_vcpus; i++)
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spin_wait_for_vcpu(i, next_iteration);
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ts_elapsed = timespec_elapsed(ts_start);
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pr_info("%-30s: %ld.%09lds\n",
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description, ts_elapsed.tv_sec, ts_elapsed.tv_nsec);
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}
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static void access_memory(struct kvm_vm *vm, int nr_vcpus,
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enum access_type access, const char *description)
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{
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perf_test_set_wr_fract(vm, (access == ACCESS_READ) ? INT_MAX : 1);
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iteration_work = ITERATION_ACCESS_MEMORY;
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run_iteration(vm, nr_vcpus, description);
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}
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static void mark_memory_idle(struct kvm_vm *vm, int nr_vcpus)
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{
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/*
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* Even though this parallelizes the work across vCPUs, this is still a
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* very slow operation because page_idle forces the test to mark one pfn
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* at a time and the clear_young notifier serializes on the KVM MMU
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* lock.
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*/
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pr_debug("Marking VM memory idle (slow)...\n");
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iteration_work = ITERATION_MARK_IDLE;
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run_iteration(vm, nr_vcpus, "Mark memory idle");
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}
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static void run_test(enum vm_guest_mode mode, void *arg)
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{
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struct test_params *params = arg;
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struct kvm_vm *vm;
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int nr_vcpus = params->nr_vcpus;
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vm = perf_test_create_vm(mode, nr_vcpus, params->vcpu_memory_bytes, 1,
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params->backing_src, !overlap_memory_access);
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perf_test_start_vcpu_threads(nr_vcpus, vcpu_thread_main);
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pr_info("\n");
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access_memory(vm, nr_vcpus, ACCESS_WRITE, "Populating memory");
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/* As a control, read and write to the populated memory first. */
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access_memory(vm, nr_vcpus, ACCESS_WRITE, "Writing to populated memory");
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access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from populated memory");
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/* Repeat on memory that has been marked as idle. */
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mark_memory_idle(vm, nr_vcpus);
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access_memory(vm, nr_vcpus, ACCESS_WRITE, "Writing to idle memory");
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mark_memory_idle(vm, nr_vcpus);
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access_memory(vm, nr_vcpus, ACCESS_READ, "Reading from idle memory");
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/* Set done to signal the vCPU threads to exit */
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done = true;
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perf_test_join_vcpu_threads(nr_vcpus);
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perf_test_destroy_vm(vm);
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}
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static void help(char *name)
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{
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puts("");
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printf("usage: %s [-h] [-m mode] [-b vcpu_bytes] [-v vcpus] [-o] [-s mem_type]\n",
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name);
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puts("");
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printf(" -h: Display this help message.");
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guest_modes_help();
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printf(" -b: specify the size of the memory region which should be\n"
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" dirtied by each vCPU. e.g. 10M or 3G.\n"
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" (default: 1G)\n");
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printf(" -v: specify the number of vCPUs to run.\n");
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printf(" -o: Overlap guest memory accesses instead of partitioning\n"
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" them into a separate region of memory for each vCPU.\n");
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backing_src_help("-s");
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puts("");
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exit(0);
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}
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int main(int argc, char *argv[])
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{
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struct test_params params = {
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.backing_src = DEFAULT_VM_MEM_SRC,
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.vcpu_memory_bytes = DEFAULT_PER_VCPU_MEM_SIZE,
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|
.nr_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.nr_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);
|
||
|
|
__TEST_REQUIRE(page_idle_fd >= 0,
|
||
|
|
"CONFIG_IDLE_PAGE_TRACKING is not enabled");
|
||
|
|
close(page_idle_fd);
|
||
|
|
|
||
|
|
for_each_guest_mode(run_test, ¶ms);
|
||
|
|
|
||
|
|
return 0;
|
||
|
|
}
|