Re: [dpdk-dev] [PATCH 0/2] net/softnic: sw fall-back for traffic management

[Thomas Monjalon <thomas@monjalon.net>]

08/06/2017 15:27, Dumitrescu, Cristian:
> Hi Thomas,
> 
> Thanks for reviewing this patch set!
> 
> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > 
> > Hi Jasvinder,
> > 
> > 26/05/2017 20:11, Jasvinder Singh:
> > > The SoftNIC PMD provides SW fall-back option for the NICs not supporting
> > > the Traffic Management (TM) features.
> > 
> > Do you mean that you want to stack PMDs in order to offer some fallbacks?
> > It means the user needs to instantiate this PMD for each HW which does
> > not support traffic management, instead of normal hardware probing?
> > 
> 
> No, the normal HW probing still takes place for the HW device. Then if QoS "probing" fails, the user can decide to create a new virtual device on top of the HW device.

What do you mean by "QoS probing"?

> > > SoftNIC PMD overview:
> > > - The SW fall-back is based on the existing librte_sched DPDK library.
> > > - The TM-agnostic port (the underlay device) is wrapped into a TM-aware
> > >   softnic port (the overlay device).
> > > - Once the overlay device (virtual device) is created, the configuration of
> > >   the underlay device is taking place through the overlay device.
> > > - The SoftNIC PMD is generic, i.e. it works for any underlay device PMD that
> > >   implements the ethdev API.
> > 
> > Why not calling librte_sched directly in ethdev for PMDs which do not
> > implement hardware offload?
> > Am I missing something obvious?
> 
> Yes, we are calling the librte_sched in ethdev, but how else can we do it?

If you call librte_sched from ethdev, that's fine.
We don't need more, do we?

> 	- We cannot change the ethdev ops of the HW device PMD because same might be used by other HW devices in the system where TM feature is not required.
> 	- We cannot change the ethdev ops of the current HW device, as on-the-fly changes of the ops structure are not allowed, right?

Right

> 	- We can create a new virtual device on top of existing HW device to inherit most of the ethdev ops of the HW device and patch some specific ethdev ops with librte_sched.
> 
> IMHO there aren't two different ways to do this.

When initializing a HW device, it can (should) reports its TM capabilities.
Then ethdev can decide to use a SW fallback if a capability is missing.