read_sched_clock
sched_clock_register(read_sched_clock, 32, sched_rate);
if (rd->read_sched_clock != arch_timer_read_counter)
u64 (*read_sched_clock)(void);
rd.read_sched_clock = read;
rd->read_sched_clock = suspended_sched_clock_read;
rd->read_sched_clock = cd.actual_read_sched_clock;
.read_sched_clock = jiffy_sched_clock_read, },
cyc = (rd->read_sched_clock() - rd->epoch_cyc) &