I found this on a page about using the Zero wit hthe preempt-RT kernel[1]
For the Zero, you also need the options:
~$ sudo nano /boot/cmdline.txt
# Add the following options:
dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0
if you are using the USB port, otherwise the Raspberry Zero freezes immediately as soon as you connect something to the port (USB drive, Wi-Fi dongle etc.)
I have not had the chance to test it yet.
[1] https://lemariva.com/blog/2018/03/raspberry-pi-zero-w-preempt-rt-kernel-performance