If the CPU reorders the eventidx read before the shadow doorbell
write, it is indeterminate whether the controller will read the
updated shadow doorbell without an MMIO write. See
https://lkml.org/lkml/2018/8/14/1031 for details.
Signed-off-by: Benjamin Saunders <bsaunders@google.com>
Change-Id: I5aa08fdd5b32c7b81e8048ca6efe546318d80b5c
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/468188
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
7188bb994f