From 7086ad6919feb2415c6027163f5c63323bcca27c Mon Sep 17 00:00:00 2001 From: Elliott Hughes Date: Thu, 19 Jun 2014 16:39:01 -0700 Subject: Cache getpid. 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 --- benchmarks/unistd_benchmark.cpp | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'benchmarks') diff --git a/benchmarks/unistd_benchmark.cpp b/benchmarks/unistd_benchmark.cpp index c35e7c3..7e2ac30 100644 --- a/benchmarks/unistd_benchmark.cpp +++ b/benchmarks/unistd_benchmark.cpp @@ -30,6 +30,17 @@ static void BM_unistd_getpid(int iters) { } BENCHMARK(BM_unistd_getpid); +static void BM_unistd_getpid_syscall(int iters) { + StartBenchmarkTiming(); + + for (int i = 0; i < iters; ++i) { + syscall(__NR_getpid); + } + + StopBenchmarkTiming(); +} +BENCHMARK(BM_unistd_getpid_syscall); + // Stop GCC optimizing out our pure function. /* Must not be static! */ pid_t (*gettid_fp)() = gettid; -- cgit v1.1