| // Copyright 2019 The ChromiumOS Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include <errno.h> |
| #include <sched.h> |
| #include <stdint.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <time.h> |
| #include <unistd.h> |
| |
| // Amount of time to spin before returning. |
| const int kSpinNs = 1e9; // 1 second |
| |
| // Number of recursive calls to make. |
| const int kRecursionDepth = 8; |
| |
| // Returns the monotonically-increasing time as nanoseconds since the epoch. |
| int64_t GetTimeNs() { |
| struct timespec ts = {0}; |
| if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0) { |
| fprintf(stderr, "clock_gettime: %s", strerror(errno)); |
| exit(1); |
| } |
| return 1e9 * ts.tv_sec + ts.tv_nsec; |
| } |
| |
| // Calls itself n times. The innermost call spins for a short period of time |
| // before returning. |
| __attribute__((noinline)) void Recurse(int n) { |
| if (n > 0) { |
| Recurse(n-1); |
| return; |
| } |
| |
| const int64_t start = GetTimeNs(); |
| while (1) { |
| if (GetTimeNs() - start >= kSpinNs) { |
| break; |
| } |
| sched_yield(); |
| } |
| } |
| |
| int main() { |
| Recurse(kRecursionDepth); |
| return 0; |
| } |