multiple processes stuck on same cpu after multiple 'fork's (Linux/C)

On a multi-core machine, why doesn't the CPU automatically move a process to a new core if there are multiple processes all on the same core at full capacity? Here is a sample program which reproduces the problem I'm seeing: ``` #include <stdio.h> #include <unistd.h> #include <stdlib.h> void RunClient(int i) { printf("Starting client %d\n", i); while (true) { } } int main(int argc, char** argv) { for (int i = 0; i < 4; ++i) { pid_t p_id = fork(); sleep(3); if (p_id == -1) { perror("fork"); } else if (p_id == 0) { RunClient(i); exit(0); } } return 0; } ``` This works as expected (when I check top, I see all 4 processes are running at 100%). However, if I remove the "sleep(3)" line, then sometimes multiple processes are set to the same CPU and thus not running at full capacity (for example, one process might be at 100% while the other 3 are each at 33%). What's going on and how do I fix it? I know I can manually set the CPU affinity, but that seems like a fragile solution?