[ovs-dev] [PATCH 1/2] docs: Clarify the superiority of dpdkvhostuserclient

[Aaron Conole]

Darrell Ball <dball at vmware.com> writes:

> On 5/26/17, 7:12 AM, "ovs-dev-bounces at openvswitch.org on behalf of Stephen Finucane" <ovs-dev-bounces at openvswitch.org on behalf of stephen at that.guru> wrote:
>
>     Apparently dpdkvhostuser interfaces are inferior to dpdkvhostuserclient.
>     Explain why.
>     
>     Signed-off-by: Stephen Finucane <stephen at that.guru>
>     Cc: Ciara Loftus <ciara.loftus at intel.com>
>     Cc: Kevin Traynor <ktraynor at redhat.com>
>     ---
>     I'd like to note what happens to traffic when OVS or a VM is restarted
>     for both port types. If someone knows the answer to this, please feel
>     free to take ownership of that patch/ask me for a v2.
>     ---
>      Documentation/topics/dpdk/vhost-user.rst | 8 ++++++--
>      1 file changed, 6 insertions(+), 2 deletions(-)
>     
>     diff --git a/Documentation/topics/dpdk/vhost-user.rst b/Documentation/topics/dpdk/vhost-user.rst
>     index ba22684..2e2396b 100644
>     --- a/Documentation/topics/dpdk/vhost-user.rst
>     +++ b/Documentation/topics/dpdk/vhost-user.rst
>     @@ -54,8 +54,12 @@ vHost User sockets, and the client connects to the server. Depending on which
>      port type you use, ``dpdkvhostuser`` or ``dpdkvhostuserclient``, a different
>      configuration of the client-server model is used.
>      
>     -For vhost-user ports, Open vSwitch acts as the server and QEMU the client.  For
>     -vhost-user-client ports, Open vSwitch acts as the client and QEMU the server.
>     +For vhost-user ports, Open vSwitch acts as the server and QEMU the client. This
>     +means if OVS dies, all VMs **must** be restarted. On the other hand, for
>     +vhost-user-client ports, OVS acts as the client and QEMU the server. This means
>     +OVS can die and be restarted without issue,
>
>
> “ and it is also possible to restart
>     +an instance itself.”
>
> Restart a VM instance ?; if so, it seems already implied.
> Or OVS instance ?
>
>  For this reason, vhost-user-client ports are the preferred
>     +type for most use cases.
>
> At one point, because I am helping to support OVS-DPDK, I had both
> vhostuser and vhostuserclient ports configured on our performance servers,
> because I thought I should have both, so I could support both. Then, I realized I
> just did not want to use vhostuser ports, due to the permissions/security
> issues, noticed on OVS restart.
>
> So, what are the use cases (besides self-flagellation) for using vhostuser ports in lieu of
> vhostuserclient ports ?

At the time they were introduced, deployed versions of qemu couldn't
support the vhostuserclient mode.  I'm less sure what the state of that
world looks like today.  I know that RHEL 7.3 doesn't ship a QEMU that
supports client-mode ports.

> If the answer is none, can we deprecate them in OVS 2.8 (update NEWS etc) and
> remove them in OVS 2.9 ?

I'm all for deprecating them as long as the major vendors (RH, Debian,
SUSE) support the newer QEMU.  2.9 may be too aggressive for removal -
perhaps the release after?  Just to be sure there is a path to migration
for existing users.

Maybe I'm off my rocker, though.

>      .. _dpdk-vhost-user:
>      
>     -- 
>     2.9.4
>     
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