Re: [dpdk-dev] [PATCH 4/4] ethdev: add helpers to move to the new offloads API

[Thomas Monjalon <thomas@monjalon.net>]

04/09/2017 16:18, Ananyev, Konstantin:
> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > 04/09/2017 15:25, Ananyev, Konstantin:
> > > Hi Shahaf,
> > >
> > > > +/**
> > > > + * A conversion function from rxmode offloads API to rte_eth_rxq_conf
> > > > + * offloads API.
> > > > + */
> > > > +static void
> > > > +rte_eth_convert_rxmode_offloads(struct rte_eth_rxmode *rxmode,
> > > > +				struct rte_eth_rxq_conf *rxq_conf)
> > > > +{
> > > > +	if (rxmode->header_split == 1)
> > > > +		rxq_conf->offloads |= DEV_RX_OFFLOAD_HEADER_SPLIT;
> > > > +	if (rxmode->hw_ip_checksum == 1)
> > > > +		rxq_conf->offloads |= DEV_RX_OFFLOAD_CHECKSUM;
> > > > +	if (rxmode->hw_vlan_filter == 1)
> > > > +		rxq_conf->offloads |= DEV_RX_OFFLOAD_VLAN_FILTER;
> > >
> > > Thinking on it a bit more:
> > > VLAN_FILTER is definitely one per device, as it would affect VFs also.
> > > At least that's what we have for Intel devices (ixgbe, i40e) right now.
> > > For Intel devices VLAN_STRIP is also per device and
> > > will also be  applied to all corresponding VFs.
> > > In fact, right now it is possible to query/change these 3 vlan offload flags on the fly
> > > (after dev_start) on  port basis by rte_eth_dev_(get|set)_vlan_offload API.
> > > So, I think at least these 3 flags need to be remained on a port basis.
> > 
> > I don't understand how it helps to be able to configure the same thing
> > in 2 places.
> 
> Because some offloads are per device, another - per queue.
> Configuring on a device basis would allow most users to conjure all
> queues in the same manner by default.
> Those users who would  need more fine-grained setup (per queue)
> will be able to overwrite it by rx_queue_setup().

Those users can set the same config for all queues.
>  
> > I think you are just describing a limitation of these HW: some offloads
> > must be the same for all queues.
> 
> As I said above - on some devices some offloads might also affect queues
> that belong to VFs (to another ports in DPDK words).   
> You might never invoke rx_queue_setup() for these queues per your app.
> But you still want to enable this offload on that device.

You are advocating for per-port configuration API because
some settings must be the same on all the ports of your hardware?
So there is a big trouble. You don't need per-port settings,
but per-hw-device settings.
Or would you accept more fine-grained per-port settings?
If yes, you can accept even finer grained per-queues settings.
> 
> > It does not prevent from configuring them in the per-queue setup.
> > 
> > > In fact, why can't we have both per port and per queue RX offload:
> > > - dev_configure() will accept RX_OFFLOAD_* flags and apply them on a port basis.
> > > - rx_queue_setup() will also accept RX_OFFLOAD_* flags and apply them on a queue basis.
> > > - if particular RX_OFFLOAD flag for that device couldn't be setup on a queue basis  -
> > >    rx_queue_setup() will return an error.
> > 
> > The queue setup can work while the value is the same for every queues.
> 
> Ok, and how people would know that?
> That for device N offload X has to be the same for all queues,
> and for device M offload X can be differs for different queues.

We can know the hardware limitations by filling this information
at PMD init.

> Again, if we don't allow to enable/disable offloads for particular queue,
> why to bother with updating rx_queue_setup() API at all? 

I do not understand this question.

> > > - rte_eth_rxq_info can be extended to provide information which RX_OFFLOADs
> > >   can be configured on a per queue basis.
> > 
> > Yes the PMD should advertise its limitations like being forced to
> > apply the same configuration to all its queues.
> 
> Didn't get your last sentence.

I agree that the hardware limitations must be written in an ethdev structure.