[ovs-dev] [PATCH] netdev-dpdk: Deprecate ring ports.

[Kevin Traynor]

On 26/11/2019 11:31, Ilya Maximets wrote:
> 'dpdkr' a.k.a. DPDK ring ports has really poor support in OVS and not
> tested on a regular basis.  These ports are intended to work via
> shared memory with another DPDK secondary process, but there are lots
> of limitations for using this functionality in practice.  Most of them
> connected with running secondary DPDK application and memory layout
> issues.  More details are available in DPDK guide:
> https://doc.dpdk.org/guides/prog_guide/multi_proc_support.html#multi-process-limitations
> 
> Beside the functional limitations it's also hard to use this
> functionality correctly.  User must be sure that OVS and secondary DPDK
> application are running on different CPU cores, which is hard because
> non-PMD threads could float over available CPU cores.  This or any
> other misconfiguration will likely lead to crash of OVS.
> 
> Another problem is that the user must actually build the secondary
> application with the same version of DPDK that was used for OVS build.
> 
> Above issues are same as we have while using DPDK pdump.
> 
> Beside that, current implementation in OVS is not able to free
> allocated rings that could lead to memory exhausting.
> 
> Initially these ports was added to use with IVSHMEM for a fast
> zero-copy HOST<-->VM communication.  However, IVSHMEM is not used
> anymore.  IVSHMEM support was removed from DPDK in 16.11 relase and
> the patch for QEMU for using regular files as a device backend is no
> longer available.  That makes DPDK ring ports barely useful in real
> virtualization environment.
> 

You could also reference that instructions for ivshmem were removed from
the OVS docs almost 3 years ago.
90ca71dd317f ("doc: Remove ivshmem instructions.")

> This patch adds a deprecation warnings for run-time port creation
> and documentation.  Claiming to completely remove this functionality
> from OVS in one of the next releases.
> 
> Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
> ---

Acked-by: Kevin Traynor <ktraynor at redhat.com>