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/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "perf_clock.h"
#include <sys/mman.h>
#include <sys/syscall.h>
#include <atomic>
#include <chrono>
#include <thread>
#include <android-base/logging.h>
#include "environment.h"
#include "event_attr.h"
#include "event_fd.h"
#include "event_type.h"
#include "record.h"
static bool perf_clock_initialized = false;
static int64_t perf_clock_and_system_clock_diff_in_ns = 0;
struct ThreadArg {
std::atomic<pid_t> thread_a_tid;
std::atomic<bool> start_mmap;
std::atomic<uint64_t> mmap_start_addr;
uint64_t system_time_in_ns;
std::atomic<bool> has_error;
};
static void ThreadA(ThreadArg* thread_arg) {
thread_arg->thread_a_tid = syscall(SYS_gettid);
while (!thread_arg->start_mmap) {
usleep(1000);
}
size_t TRY_MMAP_COUNT = 10;
struct TryMmap {
void* mmap_start_addr;
uint64_t start_system_time_in_ns;
uint64_t end_system_time_in_ns;
};
TryMmap array[TRY_MMAP_COUNT];
// In case current thread is preempted by other threads, we run mmap()
// multiple times and use the one with the smallest time interval.
for (size_t i = 0; i < TRY_MMAP_COUNT; ++i) {
array[i].start_system_time_in_ns = GetSystemClock();
array[i].mmap_start_addr =
mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (array[i].mmap_start_addr == MAP_FAILED) {
PLOG(ERROR) << "mmap() failed";
thread_arg->has_error = true;
return;
}
array[i].end_system_time_in_ns = GetSystemClock();
}
size_t best_index = 0;
uint64_t min_duration_in_ns = UINT64_MAX;
for (size_t i = 0; i < TRY_MMAP_COUNT; ++i) {
uint64_t d =
array[i].end_system_time_in_ns - array[i].start_system_time_in_ns;
if (min_duration_in_ns > d) {
min_duration_in_ns = d;
best_index = i;
}
munmap(array[i].mmap_start_addr, 4096);
}
thread_arg->mmap_start_addr =
reinterpret_cast<uint64_t>(array[best_index].mmap_start_addr);
// Perf time is generated at the end of mmap() syscall, which is close to
// the end time instead of the start time.
thread_arg->system_time_in_ns = array[best_index].end_system_time_in_ns;
}
static bool GetClockDiff(int64_t* clock_diff_in_ns) {
ThreadArg thread_arg;
thread_arg.thread_a_tid = 0;
thread_arg.start_mmap = false;
thread_arg.has_error = false;
std::thread thread_a(ThreadA, &thread_arg);
while (thread_arg.thread_a_tid == 0) {
usleep(1000);
}
std::unique_ptr<EventTypeAndModifier> event_type =
ParseEventType("cpu-clock");
if (event_type == nullptr) {
return false;
}
perf_event_attr attr = CreateDefaultPerfEventAttr(event_type->event_type);
attr.comm = 0;
attr.mmap_data = 1;
attr.mmap = 0;
attr.inherit = 0;
attr.sample_id_all = 1;
attr.freq = 0;
attr.sample_period = 1ULL << 62; // Sample records are not needed.
std::unique_ptr<EventFd> event_fd =
EventFd::OpenEventFile(attr, thread_arg.thread_a_tid, -1, nullptr);
if (event_fd == nullptr) {
return false;
}
if (!event_fd->CreateMappedBuffer(4, true)) {
return false;
}
thread_arg.start_mmap = true;
thread_a.join();
if (thread_arg.has_error) {
return false;
}
std::vector<char> buffer;
size_t buffer_pos = 0;
size_t size = event_fd->GetAvailableMmapData(buffer, buffer_pos);
std::vector<std::unique_ptr<Record>> records =
ReadRecordsFromBuffer(attr, buffer.data(), size);
uint64_t perf_time_in_ns = 0;
for (auto& r : records) {
if (r->type() == PERF_RECORD_MMAP) {
auto& record = *static_cast<MmapRecord*>(r.get());
if (record.data->addr == thread_arg.mmap_start_addr) {
perf_time_in_ns = record.Timestamp();
}
}
}
if (perf_time_in_ns == 0) {
LOG(ERROR) << "GetPerfClockAndSystemClockDiff: can't get perf time.";
return false;
}
*clock_diff_in_ns = perf_time_in_ns - thread_arg.system_time_in_ns;
LOG(VERBOSE) << "perf_time is " << perf_time_in_ns << " ns, system_time is "
<< thread_arg.system_time_in_ns << " ns , clock_diff is "
<< *clock_diff_in_ns << " ns.";
return true;
}
bool InitPerfClock() {
if (!perf_clock_initialized) {
if (!GetClockDiff(&perf_clock_and_system_clock_diff_in_ns)) {
return false;
}
perf_clock_initialized = true;
}
return true;
}
uint64_t GetPerfClock() {
CHECK(perf_clock_initialized);
return GetSystemClock() + perf_clock_and_system_clock_diff_in_ns;
}
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