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