[PATCH v3] net/af_xdp: re-enable secondary process support

[Stephen Hemminger]

On Tue, 8 Feb 2022 18:00:27 +0000
Ferruh Yigit <ferruh.yigit at intel.com> wrote:

> On 2/8/2022 5:45 PM, Stephen Hemminger wrote:
> > On Tue,  8 Feb 2022 13:48:00 +0000
> > Ciara Loftus <ciara.loftus at intel.com> wrote:
> >   
> >> +- **Secondary Processes**
> >> +
> >> +  Rx and Tx are not supported for secondary processes due to the single-producer
> >> +  single-consumer nature of the AF_XDP rings. However other operations including
> >> +  statistics retrieval are permitted.
> >> +  The maximum number of queues permitted for PMDs operating in this model is 8
> >> +  as this is the maximum number of fds that can be sent through the IPC APIs as
> >> +  defined by RTE_MP_MAX_FD_NUM.
> >> +  
> > 
> > This seems like a restriction that is true for most devices in DPDK.
> > Most other devices also have restriction that on queues;
> > the hardware descriptor ring can only be used by one thread at a time.
> > Is this different with AF_XDP?  
> 
> I asked the same on v2 :) and Ciara explained the reason, it is on v2 discussion thread.

The wording of the message is what confused me.
It would be better to change:
    due to the single-producer single-consumer nature of the AF_XDP rings
to
    due to memory mapping of the AF_XDP rings being assigned by the kernel
    in the primary process only.