Speed up map creation.
- Rewrite the Maps::Parse to use open, and a buffer on the stack.
- Rewrite the line parser away from sscanf. The current way sscanf
is used does not catch many malformed lines. In addition, this
new version improves performance by 50% over sscanf on sailfish.
- Add a lot of unit tests for the parser to make sure there are
no problems. In addition, add a special line that was not rejected
with the previous version of the code.
- Add new accessor to get the map at a particular index.
- Add a backtrace benchmark for map creation for both new and old.
This cl results in ~5% speedup and makes the new unwinder map creation
about the same for 64 bit. It's still a bit slower, but not by much.
On 32 bit, we are still about 5% slower than the old creation method,
though.
Bug: 23762183
Test: libunwindstack unit tests pass. Ran the new benchmarks.
Change-Id: Id4431e539f400984e6fad62153fdf4152d518322
diff --git a/libbacktrace/backtrace_benchmarks.cpp b/libbacktrace/backtrace_benchmarks.cpp
new file mode 100644
index 0000000..30c2a55
--- /dev/null
+++ b/libbacktrace/backtrace_benchmarks.cpp
@@ -0,0 +1,162 @@
+/*
+ * Copyright (C) 2017 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 <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <string>
+
+#include <android-base/file.h>
+
+#include <benchmark/benchmark.h>
+
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
+// Definitions of prctl arguments to set a vma name in Android kernels.
+#define ANDROID_PR_SET_VMA 0x53564d41
+#define ANDROID_PR_SET_VMA_ANON_NAME 0
+
+constexpr size_t kNumMaps = 2000;
+constexpr size_t kNumIterations = 1000;
+
+static bool CountMaps(pid_t pid, size_t* num_maps) {
+ // Minimize the calls that might allocate memory. If too much memory
+ // gets allocated, then this routine will add extra maps and the next
+ // call will fail to get the same number of maps as before.
+ int fd =
+ open((std::string("/proc/") + std::to_string(pid) + "/maps").c_str(), O_RDONLY | O_CLOEXEC);
+ if (fd == -1) {
+ fprintf(stderr, "Cannot open map file for pid %d: %s\n", pid, strerror(errno));
+ return false;
+ }
+ *num_maps = 0;
+ while (true) {
+ char buffer[2048];
+ ssize_t bytes = read(fd, buffer, sizeof(buffer));
+ if (bytes <= 0) {
+ break;
+ }
+ // Count the '\n'.
+ for (size_t i = 0; i < static_cast<size_t>(bytes); i++) {
+ if (buffer[i] == '\n') {
+ ++*num_maps;
+ }
+ }
+ }
+
+ close(fd);
+ return true;
+}
+
+static void CreateMap(benchmark::State& state, BacktraceMap* (*map_func)(pid_t, bool)) {
+ state.PauseTiming();
+ // Create a remote process so that the map data is exactly the same.
+ // Also, so that we can create a set number of maps.
+ pid_t pid;
+ if ((pid = fork()) == 0) {
+ size_t num_maps;
+ if (!CountMaps(getpid(), &num_maps)) {
+ exit(1);
+ }
+ // Create uniquely named maps.
+ std::vector<void*> maps;
+ for (size_t i = num_maps; i < kNumMaps; i++) {
+ int flags = PROT_READ | PROT_WRITE;
+ // Alternate page type to make sure a map entry is added for each call.
+ if ((i % 2) == 0) {
+ flags |= PROT_EXEC;
+ }
+ void* memory = mmap(nullptr, PAGE_SIZE, flags, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (memory == MAP_FAILED) {
+ fprintf(stderr, "Failed to create map: %s\n", strerror(errno));
+ exit(1);
+ }
+ memset(memory, 0x1, PAGE_SIZE);
+ if (prctl(ANDROID_PR_SET_VMA, ANDROID_PR_SET_VMA_ANON_NAME, memory, PAGE_SIZE, "test_map") ==
+ -1) {
+ fprintf(stderr, "Failed: %s\n", strerror(errno));
+ }
+ maps.push_back(memory);
+ }
+
+ if (!CountMaps(getpid(), &num_maps)) {
+ exit(1);
+ }
+
+ if (num_maps != kNumMaps) {
+ fprintf(stderr, "Maps set incorrectly: %zu found, %zu expected.\n", num_maps, kNumMaps);
+ std::string str;
+ android::base::ReadFileToString("/proc/self/maps", &str);
+ fprintf(stderr, "%s\n", str.c_str());
+ exit(1);
+ }
+
+ // Wait for an hour at most.
+ sleep(3600);
+ exit(1);
+ } else if (pid < 0) {
+ fprintf(stderr, "Fork failed: %s\n", strerror(errno));
+ return;
+ }
+
+ size_t num_maps = 0;
+ for (size_t i = 0; i < 2000; i++) {
+ if (CountMaps(pid, &num_maps) && num_maps == kNumMaps) {
+ break;
+ }
+ usleep(1000);
+ }
+ if (num_maps != kNumMaps) {
+ fprintf(stderr, "Timed out waiting for the number of maps available: %zu\n", num_maps);
+ return;
+ }
+
+ state.ResumeTiming();
+ while (state.KeepRunning()) {
+ for (size_t i = 0; i < static_cast<size_t>(state.range(0)); i++) {
+ BacktraceMap* map = map_func(pid, false);
+ if (map == nullptr) {
+ fprintf(stderr, "Failed to create map\n");
+ return;
+ }
+ delete map;
+ }
+ }
+ state.PauseTiming();
+
+ kill(pid, SIGKILL);
+ waitpid(pid, nullptr, 0);
+}
+
+static void BM_create_map(benchmark::State& state) {
+ CreateMap(state, BacktraceMap::Create);
+}
+BENCHMARK(BM_create_map)->Arg(kNumIterations);
+
+static void BM_create_map_new(benchmark::State& state) {
+ CreateMap(state, BacktraceMap::CreateNew);
+}
+BENCHMARK(BM_create_map_new)->Arg(kNumIterations);
+
+BENCHMARK_MAIN();