pg_ev_thread_swtch
pg_ev_thread_swtch(cp, gethrtime_unscaled(), cp->cpu_idle_thread,
pg_ev_thread_swtch(cpu, gethrtime_unscaled(), curthread, next);
pg_ev_thread_swtch(cp, now, curthread, next);
pg_ev_thread_swtch(cp, now, t, next);
void pg_ev_thread_swtch(cpu_t *, hrtime_t, kthread_t *, kthread_t *);