Comment by limoce

  I am not 100% sure that all of the mitigation overhead 
  comes from syscalls, but it stands to reason that a lot 
  of it arises from security hardening in user-to-kernel 
  and kernel-to-user transitions.

Will io_uring be also affected by Spectre mitigations given it has eliminated most kernel/user switches?

And did anyone do a head-to-head comparison between io_uring and DPDK?