7086ad6919
In practice, with this implementation we never need to make a system call. We get the main thread's tid (which is the same as our pid) back from the set_tid_address system call we have to make during initialization. A new pthread will have the same pid as its parent, and a fork child's main (and only) thread will have a pid equal to its tid, which we get for free from the kernel before clone returns. The only time we'd actually have to make a getpid system call now is if we take a signal during fork and the signal handler calls getpid. (That, or we call getpid in the dynamic linker while it's still dealing with its own relocations and hasn't even set up the main thread yet.) Bug: 15387103 Change-Id: I6d4718ed0a5c912fc75b5f738c49a023dbed5189
68 lines
1.5 KiB
C++
68 lines
1.5 KiB
C++
/*
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* Copyright (C) 2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "benchmark.h"
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#include <sys/syscall.h>
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#include <unistd.h>
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static void BM_unistd_getpid(int iters) {
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StartBenchmarkTiming();
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for (int i = 0; i < iters; ++i) {
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getpid();
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}
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StopBenchmarkTiming();
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}
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BENCHMARK(BM_unistd_getpid);
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static void BM_unistd_getpid_syscall(int iters) {
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StartBenchmarkTiming();
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for (int i = 0; i < iters; ++i) {
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syscall(__NR_getpid);
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}
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StopBenchmarkTiming();
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}
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BENCHMARK(BM_unistd_getpid_syscall);
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// Stop GCC optimizing out our pure function.
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/* Must not be static! */ pid_t (*gettid_fp)() = gettid;
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static void BM_unistd_gettid(int iters) {
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StartBenchmarkTiming();
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for (int i = 0; i < iters; ++i) {
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gettid_fp();
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}
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StopBenchmarkTiming();
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}
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BENCHMARK(BM_unistd_gettid);
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static void BM_unistd_gettid_syscall(int iters) {
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StartBenchmarkTiming();
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for (int i = 0; i < iters; ++i) {
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syscall(__NR_gettid);
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}
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StopBenchmarkTiming();
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}
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BENCHMARK(BM_unistd_gettid_syscall);
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