Re: [RFC PATCH v2 3/5] librte_ether: add API's for VF management

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Sep 27, 2016 at 11:31:06AM +0100, Iremonger, Bernard wrote:
> Hi Thomas, Bruce,
> 
> <snip>
> 
> > Subject: Re: [dpdk-dev] [RFC PATCH v2 3/5] librte_ether: add API's for VF
> > management
> > 
> > 2016-09-26 15:37, Iremonger, Bernard:
> > > Hi Thomas, Bruce,
> > >
> > > <snip>
> > >
> > > > Subject: Re: [dpdk-dev] [RFC PATCH v2 3/5] librte_ether: add API's
> > > > for VF management
> > > >
> > > > 2016-09-23 17:02, Iremonger, Bernard:
> > > > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > > > > 2016-09-23 09:53, Richardson, Bruce:
> > > > > > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > > > > > > 2016-09-23 10:20, Bruce Richardson:
> > > > > > > > > On Thu, Sep 22, 2016 at 07:04:37PM +0200, Thomas Monjalon
> > wrote:
> > > > > > > > > > 2016-09-15 16:46, Iremonger, Bernard:
> > > > > > > > > > > > > > Do we really need to expose VF specific functions
> > here?
> > > > > > > > > > > > > > It can be generic(PF/VF) function indexed only
> > > > > > > > > > > > > > through
> > > > > > > > port_id.
> > > > > > > > > > > > > > (example: as
> > > > > > > > > > > > > > rte_eth_dev_set_vlan_anti_spoof(uint8_t
> > > > > > > > > > > > > > port_id, uint8_t on)) For instance, In Thunderx
> > > > > > > > > > > > > > PMD, We are not exposing a separate port_id for
> > > > > > > > > > > > > > PF. We only enumerate 0..N VFs as 0..N ethdev
> > > > > > > > > > > > > > port_id
> > > > > > > > > > > > >
> > > > > > > > > > > > > Our intention with this patch is to control the VF from the
> > PF.
> > > > > > > > > > > > >
> > > > > > > > > > > > > The following librte_ether functions already work
> > > > > > > > > > > > > in a similar
> > > > > > > > way:
> > > > > > > > > > > > >
> > > > > > > > > > > > > rte_eth_dev_set_vf_rxmode(uint8_t port_id,
> > > > > > > > > > > > > uint16_t vf, uint16_t rx_mode, uint8_t on)
> > > > > > > > > > > > >
> > > > > > > > > > > > > rte_eth_dev_set_vf_rx(uint8_t port_id, uint16_t
> > > > > > > > > > > > > vf, uint8_t
> > > > > > > > > > > > > on)
> > > > > > > > > > > > >
> > > > > > > > > > > > > rte_eth_dev_set_vf_tx(uint8_t port_id, uint16_t
> > > > > > > > > > > > > vf, uint8_t
> > > > > > > > > > > > > on)
> > > > > > > > > > > > >
> > > > > > > > > > > > > int rte_eth_set_vf_rate_limit(uint8_t port_id,
> > > > > > > > > > > > > uint16_t vf, uint16_t tx_rate, uint64_t q_msk)
> > > > > > > > > > > >
> > > > > > > > > > > > I have a bad feeling with these functions dedicated
> > > > > > > > > > > > to VF from
> > > > PF.
> > > > > > > > > > > > Are we sure there is no other way?
> > > > > > > > > > > > I mean we just need to know the VF with a port ID.
> > > > > > > > > > >
> > > > > > > > > > > When the VF is used in a VM the port ID of the VF is
> > > > > > > > > > > not visible to
> > > > > > > > the PF.
> > > > > > > > > > > I don't think there is another way to do this.
> > > > > > > > > >
> > > > > > > > > > I don't understand why we could not assign a port id to
> > > > > > > > > > the VF from the host instead of having the couple PF port id /
> > VF id.
> > > > > > > > > > Can we enumerate all the VFs associated to a PF?
> > > > > > > > > > Then can we allocate them a port id in the array
> > rte_eth_devices?
> > > > > > > > >
> > > > > > > > > Hi Thomas,
> > > > > > > > >
> > > > > > > > > The VF is not a port visible to DPDK, though, so it
> > > > > > > > > shouldn't have a port id IMHO. DPDK can't actually do anything
> > with it.
> > > > > > > >
> > > > > > > > You say the contrary below.
> > > > > > >
> > > > > > > Well, yes and no. The driver can manipulate things for the VF,
> > > > > > > but DPDK
> > > > > > doesn't actually have a device that corresponds to the VF. There
> > > > > > are no PCI bar mappings for it, DPDK can't do RX and TX with it etc.?
> > > > > >
> > > > > > Very good point.
> > > > > > There are only few ethdev functions which are supported by every
> > > > > > drivers, like Rx/Tx and would not be available for VF from PF
> > interface.
> > > > > >
> > > > > > > > > The PCI device for the VF is likely passed through to a
> > > > > > > > > different VM and being used there. Unfortunately, the VF
> > > > > > > > > still needs certain things done for it by the PF, so if
> > > > > > > > > the PF is under DPDK control, it needs to provide the
> > > > > > > > > functionality to assist
> > > > the VF.
> > > > > > > >
> > > > > > > > Why not have a VF_from_PF driver which does the mailbox
> > things?
> > > > > > > > So you can manage the VF from the PF with a simple port id.
> > > > > > > > It really seems to be the cleanest design to me.
> > > > > > >
> > > > > > > While I see your point, and it could work, I just want to be
> > > > > > > sure that we are
> > > > > > ok with the results of that. Suppose we do create ethdevs for
> > > > > > the VFs controlled by the PF. Does the new VF get counted in the
> > > > > > rte_eth_dev_count() value (I assume yes)? How are apps meant to
> > > > > > use the port? Do they have to put in a special case when
> > > > > > iterating through all the port ids to check that it's not a
> > > > > > pseudo port that can't do anything. None of the standard ethdev
> > > > > > calls from an app will work on it, you can't configure nb rx/tx
> > > > > > queues on it, you can't start or
> > > > stop it, you can't do rx or tx on it, etc, etc.
> > > > > >
> > > > > > Yes these devices would be special because their supported API
> > > > > > would be quite different. I was thinking that in the future you
> > > > > > could add most of the configuration functions through the VF
> > mailbox.
> > > > > > But the Intel mailbox currently support only some special
> > > > > > configurations which are not supported by other devices even its
> > > > > > own VF device (except setting MAC address).
> > > > > > And when I read "set drop enable bit in the VF split rx control
> > > > > > register", it becomes clear it is really specific and has
> > > > > > nothing to do in the generic ethdev API.
> > > > > > That's why it is a NACK.
> > > > > >
> > > > > > When we want to use these very specific features we are aware of
> > > > > > the underlying device and driver. So we can directly include a
> > > > > > header from the driver. I suggest to retrieve a handler for the
> > > > > > device which is not a port id and will allow to call ixgbe functions
> > directly.
> > > > > > It could be achieved by adding an ethdev function like discussed here:
> > > > > > 	http://dpdk.org/ml/archives/dev/2016-September/047392.html
> > > > > >
> > > > >
> > > > > I have been reading the net/vhost mail thread above. The following
> > > > > quote
> > > > is from this thread.
> > > > >
> > > > > "It means I would be in favor of introducing API in drivers for
> > > > > very specific
> > > > features."
> > > > >
> > > > > At present all the PMD functions are accessed through the
> > > > > eth_dev_ops
> > > > structure, there are no PMD API's.
> > > > >
> > > > > Is your proposal to add API(s) to the DPDK ixgbe PMD (similar to a
> > > > > driver
> > > > ioctl API) which can be accessed through a generic API in the ethdev?
> > > >
> > > > Not exactly. I'm thinking about a PMD specific API.
> > > > The only ethdev API you need would be a function to retrieve a
> > > > handler (an opaque pointer on the device struct) from the port id.
> > > > Then you can include rte_ixgbe.h and directly call the specific
> > > > ixgbe function, passing the device handler.
> > > > How does it sound?
> > >
> > > I have been prototyping this proposed solution, it appears to work.
> > >
> > > I have added the following function:
> > >
> > > int  rte_eth_dev_get_pmd_handle(uint8_t port_id, void** pmd_handle);
> > >
> > > The pmd_handle is a pointer to a dev_ops structure containing driver
> > specific functions.
> > >
> > > Using the pmd_handle the driver specific functions can be called
> > > (without having them in struct eth_dev_ops)
> > >
> > > Has this proposal been superseded by the discussion on the following
> > patch?
> > >
> > > [PATCH] net/vhost: Add function to retreive the 'vid' for a given port
> > > id
> > 
> > Maybe, it can be superseded by this discussion, yes.
> > Bruce thinks we do not need rte_eth_dev_get_pmd_handle().
> > What is your opinion about using port_id directly and retrieving the structs
> > from the driver via rte_eth_devices?
> 
> Looking at the code in rte_eth_devices[]
> 
> struct rte_eth_dev  rte_eth_devices[RTE_MAX_ETHPORTS];
> 
> struct rte_eth_dev {
> 
> ...
> 
> const struct eth_dev_ops *dev_ops; /**< Functions exported by PMD */ 
> 
> ...
> 
>  void *pmd_ops;  /** < exported PMD specific functions */ 
>   
> }
> 
> The PMD functions are only accessible at present if they are in struct eth_dev_ops.
> 
> Adding a pmd_ops field to struct rte_eth_dev {} makes the PMD functions accessible and is a simpler solution than using rte_eth_dev_get_pmd_handle() to get access to the PMD functions.
> 
> Regards,
> 

Why would an ops structure be needed? If it's a private API for a driver, there
should be no need for function pointers, and instead the driver can define
regular functions in it's header file, no?

/Bruce