[dpdk-dev] [PATCH 3/3] net/virtio: reject unsupported Rx multi queue modes

[David Marchand]

On Thu, Oct 10, 2019 at 10:14 AM Andrew Rybchenko
<arybchenko at solarflare.com> wrote:
>
> On 10/10/19 10:42 AM, Thomas Monjalon wrote:
> > 09/10/2019 13:24, Andrew Rybchenko:
> >> On 10/9/19 1:41 PM, Tiwei Bie wrote:
> >>> My understanding is that, setting mq_mode to ETH_MQ_RX_NONE means
> >>> no method is enforced on how to route packets to MQs.
> >> I'm not sure. It is definitely a place to be improved in
> >> ethdev documentation. Thomas, Ferruh, what do you think?
> >> Is it really a definition of ETH_MQ_RX_NONE?
> > I think it means everything go to queue 0.
>
> I understand it this way as well.
>
> > The comment says no DCB, RSS or VMDQ.
> > It looks like the "NONE" value has been abused for some custom steering.
> > We have two options:
> >       - document NONE as a possible case of custom steering
> >       - add a new CUSTOM value
>
> I'd prefer to say that ETH_MQ_RX_RSS with rss_hf equal to 0 means
> unspecified/unknown steering. If application just want to spread
> traffic across many Rx queues, it is natural choice to say that
> it want RSS, but do not care about spreading algorithm etc.
> It allows driver use recommended defaults if rss_hf is controllable,
> or just spread in virtio case.

RSS is about maintaining affinity of a "flow" (as in packets sharing
the same l3/l4 tuples) to a specific queue.
Here, we can have packets from a same flow on any queue depending on
what happened on the vhost side.

I prefer we describe this behavior as something else than RSS.


-- 
David Marchand