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- // Copyright 2022 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #include "base/android/thread_instruction_count.h"
- #include "base/check_op.h"
- #include "base/logging.h"
- #include "base/no_destructor.h"
- #include "base/numerics/safe_conversions.h"
- #include "base/threading/thread_local_storage.h"
- #include <linux/perf_event.h>
- #include <sys/syscall.h>
- #include <unistd.h>
- namespace base {
- namespace android {
- namespace {
- constexpr int kPerfFdOpenFailed = -1;
- ThreadLocalStorage::Slot& InstructionCounterFdSlot() {
- static NoDestructor<ThreadLocalStorage::Slot> fd_slot([](void* fd_ptr) {
- int fd = checked_cast<int>(reinterpret_cast<intptr_t>(fd_ptr));
- if (fd > 0)
- close(fd);
- });
- return *fd_slot;
- }
- // Opens a new file descriptor that emits the value of
- // PERF_COUNT_HW_INSTRUCTIONS in userspace (excluding kernel and hypervisor
- // instructions) for the given |thread_id|, or 0 for the calling thread.
- //
- // Returns kPerfFdOpenFailed if opening the file descriptor failed.
- int OpenInstructionCounterFdForThread(int thread_id) {
- struct perf_event_attr pe = {0};
- pe.type = PERF_TYPE_HARDWARE;
- pe.size = sizeof(struct perf_event_attr);
- pe.config = PERF_COUNT_HW_INSTRUCTIONS;
- pe.exclude_kernel = 1;
- pe.exclude_hv = 1;
- long fd = syscall(__NR_perf_event_open, &pe, thread_id, /* cpu */ -1,
- /* group_fd */ -1, /* flags */ 0);
- if (fd < 0) {
- PLOG(ERROR) << "perf_event_open: omitting instruction counters";
- return kPerfFdOpenFailed;
- }
- return checked_cast<int>(fd);
- }
- // Retrieves the active perf counter FD for the current thread, performing
- // lazy-initialization if necessary.
- int InstructionCounterFdForCurrentThread() {
- auto& slot = InstructionCounterFdSlot();
- int fd = checked_cast<int>(reinterpret_cast<intptr_t>(slot.Get()));
- if (fd == 0) {
- fd = OpenInstructionCounterFdForThread(0);
- slot.Set(reinterpret_cast<void*>(fd));
- }
- return fd;
- }
- } // namespace
- // static
- bool ThreadInstructionCount::IsSupported() {
- return InstructionCounterFdForCurrentThread() > 0;
- }
- // static
- ThreadInstructionCount ThreadInstructionCount::Now() {
- DCHECK(IsSupported());
- int fd = InstructionCounterFdForCurrentThread();
- if (fd <= 0)
- return ThreadInstructionCount();
- uint64_t instructions = 0;
- ssize_t bytes_read = read(fd, &instructions, sizeof(instructions));
- CHECK_EQ(bytes_read, static_cast<ssize_t>(sizeof(instructions)))
- << "Short reads of small size from kernel memory is not expected. If "
- "this fails, use HANDLE_EINTR.";
- return ThreadInstructionCount(instructions);
- }
- } // namespace android
- } // namespace base
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