1 #include <inttypes.h>
2 #include <sys/types.h>
3 #include <time.h>
4 #include <unistd.h>
5 
6 #define noinline __attribute__((__noinline__))
7 
GetSystemClock()8 static inline uint64_t GetSystemClock() {
9   timespec ts;
10   // Assume clock_gettime() doesn't fail.
11   clock_gettime(CLOCK_MONOTONIC, &ts);
12   return ts.tv_sec * 1000000000ULL + ts.tv_nsec;
13 }
14 
15 constexpr int LOOP_COUNT = 100000000;
RunFunction()16 uint64_t noinline RunFunction() {
17   uint64_t start_time_in_ns = GetSystemClock();
18   for (volatile int i = 0; i < LOOP_COUNT; ++i) {
19   }
20   return GetSystemClock() - start_time_in_ns;
21 }
22 
SleepFunction(unsigned long long sleep_time_in_ns)23 uint64_t noinline SleepFunction(unsigned long long sleep_time_in_ns) {
24   uint64_t start_time_in_ns = GetSystemClock();
25   struct timespec req;
26   req.tv_sec = sleep_time_in_ns / 1000000000;
27   req.tv_nsec = sleep_time_in_ns % 1000000000;
28   nanosleep(&req, nullptr);
29   return GetSystemClock() - start_time_in_ns;
30 }
31 
GlobalFunction()32 void noinline GlobalFunction() {
33   uint64_t total_sleep_time_in_ns = 0;
34   uint64_t total_run_time_in_ns = 0;
35   while (true) {
36     total_run_time_in_ns += RunFunction();
37     if (total_sleep_time_in_ns < total_run_time_in_ns) {
38       total_sleep_time_in_ns += SleepFunction(total_run_time_in_ns - total_sleep_time_in_ns);
39     }
40   }
41 }
42 
main()43 int main() {
44   GlobalFunction();
45   return 0;
46 }
47