AF_XDP sendto kick returning EPERM

Hi,

I'm using sendto() to kick tx in my AF_XDP program after I submit
descriptors to the tx ring -

ret = sendto(xsk_socket__fd(xsk_), NULL, 0, MSG_DONTWAIT, NULL, 0);

However, I'm receiving EPERM as the return value every time. AFAIK
this is not an expected return value. Since this is with i40e, I
checked i40e_xsk_wakeup() - but that also doesn't return EPERM. I am
running as root and I don't see any problems with creating the xsk,
configuring umem etc.

Also, no packets seem to go out either.

# uname -a
Linux Ostinato-1 5.11.15-1-default #1 SMP Fri Apr 16 16:47:34 UTC 2021
(64fb5bf) x86_64 x86_64 x86_64 GNU/Linux

I don't see the problem on another machine with i40e but older kernel 5.4 series

Any suggestions on what to look for or how to proceed?

Srivats