Re: [dpdk-dev] [PATCH] net/af_xdp: fix support of secondary process

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

> > > > >
> > > > > Doing basic operations like info_get or get_stats was broken
> > > > > in af_xdp PMD. The info_get would crash because dev->device
> > > > > was NULL in secondary process. Fix this by doing same initialization
> > > > > as af_packet and tap devices.
> > > > >
> > > > > The get_stats would crash because the XDP socket is not open in
> > > > > primary process. As a workaround don't query kernel for dropped
> > > > > packets when called from secondary process.
> > > > >
> > > > > Note: this does not address the other bug which is that transmitting
> > > > > in secondary process is broken because the send() in tx_kick
> > > > > will fail because XDP socket fd is not valid in secondary process.
> > > >
> > > > Hi Stephen,
> > > >
> > > > Apologies for the delayed reply, I was on vacation.
> > > >
> > > > In the Bugzilla report you suggest we:
> > > > "mark AF_XDP as broken in with primary/secondary
> > > > and return an error in probe in secondary process".
> > > > I agree with this suggestion. However with this patch we still permit
> > > secondary, and just make sure it doesn't crash for get_stats. Did you
> change
> > > your mind?
> > > > Personally, I would prefer to have primary/secondary either working
> 100%
> > > or else not allowed at all by throwing an error during probe. What do you
> > > think? Do you have a reason/use case to permit secondary processes
> despite
> > > some features not being available eg. full stats, tx?
> > > >
> > > > Thanks,
> > > > Ciara
> > >
> > > There are two cases where secondary is useful even if send/receive can't
> > > work from secondary process.
> > > The pdump and proc-info applications can work with these patches.
> > >
> > > I am using XDP over pdump as an easy way to get packets into the code
> for
> > > testing.
> > >
> > > The flag in the documentation doesn't have a "limited" version.
> > > If you want, will send another patch to disable secondary support.
> >
> > Thanks for explaining. Since there are use cases for secondary, even if the
> functionality is limited, I don't think it should be disabled.
> > Since we can't flag it as 'limited' in the feature matrix, could you please add
> a note about the send/receive limitation in the AF_XDP PMD documentation
> in a v2? There are already a number of limitations listed, which you can add
> to.
> >
> > Thanks,
> > Ciara
> >
> > >
> > > Supporting secondary, means adding a mechanism to pass the socket
> > > around.
> 
> Looking at this in more detail, and my recommendation is:
> For 21.11 release (and mark it as Fixes so it gets backported). Have the driver
> return -ENOTSUP in secondary process.
> 
> For 22.03 add real secondary support using the rte_mp_msg to pass
> necessary
> state to secondary process. Includes socket (and other memory regions?).
> 
> The pdump and proc-info cases are only useful for developer testing, and
> there are
> other ways to do the same thing.


+1 that sounds reasonable to me.

Thanks,
Ciara