On Wed, Sep 13, 2017 at 04:17:37PM +0000, Darrell Ball wrote:
>
>
> On 9/13/17, 2:57 AM, "Simon Horman" <[email protected]> wrote:
>
> On Tue, Sep 12, 2017 at 08:36:19AM +0000, Darrell Ball wrote:
> >
> > On 9/10/17, 11:14 PM, "[email protected] on behalf of
> Yuanhan Liu" <[email protected] on behalf of
> [email protected]> wrote:
> >
> > On Fri, Sep 08, 2017 at 06:48:50PM +0200, Simon Horman wrote:
> > > On Tue, Sep 05, 2017 at 05:22:59PM +0800, Yuanhan Liu wrote:
> > > > From: Finn Christensen <[email protected]>
> > > >
> > > > AFAIK, most (if not all) NICs (including Mellanox and Intel) do
> not
> > > > support a pure MARK action. It's required to be used together
> with
> > > > some other actions, like QUEUE.
> > > >
> > > > To workaround it, retry with a queue action when first try
> failed.
> > > >
> > > > Moreover, some Intel's NIC (say XL710) needs the QUEUE action
> set
> > > > before the MARK action.
> > > >
> > > > Co-authored-by: Yuanhan Liu <[email protected]>
> > > > Signed-off-by: Finn Christensen <[email protected]>
> > > > Signed-off-by: Yuanhan Liu <[email protected]>
> > >
> > > This feels a bit like the tail wagging the dog.
> > > Is this the lowest level at which it makes sense to implement
> > > this logic?
> > >
> > > If so then I wonder if some sort of probing would be in order
> > > to avoid the cost of trying to add the flow twice to hardware
> > > where the queue is required.
> >
> > Do you mean something like rte_flow capability query, like whether
> > a queue action is needed for a mark action? If so, yes, I do think
> > we miss an interface like this.
> >
> > Note that even in this solution, the flow won't be created twice
> > to the hardware, because the first try would be failed.
> >
> > [Darrell]
> >
> > Having an api to quey capability and avoid the first try
> to HW would be nice, but there are dependencies
> > on RTE, drivers etc and I don’t know definitive the api
> would be.
> >
> > Also, as nics are added this capability needs to be done
> and state needs to be kept in all cases.
> >
> > It is an enhancement and if done should be reliable.
>
> Agreed. Though I was more thinking of probing the hardware rather than
> having a capability API - I expect this would remove several of the
> dependencies you describe above.
>
>
> [Darrell] I have been pondering the probing option as well. It is certainly a
> valid option;
After thinking twice, I do think the probing might be better than capability
feedback in some cases. For example, it makes more sense to probe the "mark
and queue" actions than asking DPDK to provide such ability. It's more like
a combination, which is hard to give from DPDK side.
But for some cases, like do the underlaying NIC support a (few) specifics
actions, or a (few) protocols, it's more clean and easier to provide cap
feedback API from DPDK, IMO.
> we use it in other cases such as datapath probing. One of the aspects that
> worries me here is
> maintaining the correct per interface (essentially; although the attribute is
> per nic) state
> across various events such as new ports being added, vswitchd restarts, races
> with flow
> creation. It would be non-trivial I guess and probably appropriate for the
> next patch series, if done.
I would think so. I will think about it after this patchset, to see which one
suits better for our case. Or maybe, we could have both: I do think it makes
sense to let DPDK to provide some basic capability feedbacks, for example,
the supported actions, protocols, etc.
> In this case, we have what seems like a clear distinction b/w Napatech which
> does not need the
> queue action workaround and everything else, which does.
> Besides the non-Napatech behavior, which is worrisome, maintaining the
> difference for flow handling
> under the covers is concerning.
>
> I wonder if we should be upfront as possible here and just have a dpdk
> interface configuration – maybe
> something like “supports native HWOL mark action” since the better behavior
> is the exception?
> The interface config would be more robust than probing.
> This would need documentation, of course.
The thing is that the option is fixed, while the NIC driver may change.
Such option may apply to old versions may not apply to newer versions.
> I think anyways we need documentation describing the difference b/w nics in
> the dpdk documentation (howto part).
IIRC, there was already an ask from the DPDK mailing list.
--yliu
> Assuming no such enhancement is appropriate at this time I would
> still like to ask if this is the best place for this hardware-specific
> code?
>
> [Darrell]
>
> For OVS, the netdev-dpdk layer is the lowest layer.
> This kind of workaround is hard to hide, since we are messing with the rxq,
> so I think OVS needs to know
> that it is in effect anyways. An alternative is to supply a mark and an
> ‘optional queue’ and let the driver decide if the queue is
> needed and report back whether it was. This would be hard to do across
> various drivers. Supporting in the rte layer would require both
> rte and driver support, so even more support.
>
>
>
> > A separate comment is we need to document which nics need
> the queue action.
> >
> > Also, I think we should check errno in the present code.
>
>
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