Re: [dpdk-dev] Should we disallow running secondaries after primary has died?

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Bruce Richardson
> Sent: Friday, July 26, 2019 10:40 AM
> To: Burakov, Anatoly <anatoly.burakov@intel.com>
> Cc: dev@dpdk.org; Thomas Monjalon <thomas@monjalon.net>
> Subject: Re: [dpdk-dev] Should we disallow running secondaries after primary has died?
> 
> On Fri, Jul 26, 2019 at 10:05:02AM +0100, Burakov, Anatoly wrote:
> > Hi all,
> >
> > While investigating this bug:
> >
> > https://bugs.dpdk.org/show_bug.cgi?id=284
> >
> > I came across a realization that, when primary process dies, very little
> > actually works. There are some documented issues that are already present
> > when secondary processes keep running, like memory map becoming static, and
> > hotplug not working any more.
> >
> > What is less known (and documented) is that VFIO also completely stops
> > working when initializing processes, because some time since 18.xx releases,
> > we've fixed a long standing VFIO-related bug that had to do with creating
> > new containers every time a secondary is run - secondary processes will now
> > reuse the primary process's container instead.
> >
> > Meaning, for VFIO devices, secondary process *initialization* will fail
> > after primary process has died, because there is no longer a process from
> > which we can get the VFIO container from. Things will still sort-of work
> > with igb_uio or in vfio-noiommu mode, but again - no memory map updates, no
> > hotplug, potentially other things that i don't even know about.
> >
> > Therefore, while ideally we would like people to have primary process always
> > running, the least we can do to avoid documenting a complex matrix of "what
> > is supported in which case" is to disallow secondary process initialization
> > after primary process has died.
> >
> > ("disallow" as in "explicitly document it as unsupported", although we can
> > also outright prevent it if we want - rte_eal_primary_proc_alive() will tell
> > us that)
> >
> Documenting this limitation seems a good thing to do. I'm not sure that
> it's worthwhile trying to make the scenario (of running a secondary after a
> primary has terminated) supported.
> 
> /Bruce

NP to disallow it.
In fact, I think it would be easier for everyone just to drop current DPDK MP model,
and keep just standalone DPDK instances.