alarm_forward_now
u64 ticks = alarm_forward_now(&ctx->t.alarm, ctx->tintv) - 1;
alarm_forward_now(&ctx->t.alarm, ctx->tintv);
u64 alarm_forward_now(struct alarm *alarm, ktime_t interval);
EXPORT_SYMBOL_GPL(alarm_forward_now);
timr->it_overrun += alarm_forward_now(alarm, timr->it_interval);