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

["Loftus, Ciara" <ciara.loftus@intel.com>]

> 
> On 2/8/2022 6:42 PM, Stephen Hemminger wrote:
> > On Tue, 8 Feb 2022 18:00:27 +0000
> > Ferruh Yigit <ferruh.yigit@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@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.
> 
> +1

Agree, I worded this poorly! Will submit a v4 with a more accurate explanation of the limitation.

Thanks,
Ciara