Re: [dpdk-dev] [PATCH v2] examples/client_server_mp: check port ownership

[Matan Azrad <matan@mellanox.com>]

Hi Stephen

From: Stephen Hemminger
> On Mon, 8 Jul 2019 06:37:14 +0000
> Matan Azrad <matan@mellanox.com> wrote:
> 
> > Hi Stephen
> >
> > From: Stephen Hemminger
> > > Sent: Sunday, July 7, 2019 7:47 PM
> > > To: Matan Azrad <matan@mellanox.com>
> > > Cc: anatoly.burakov@intel.com; dev@dpdk.org; Stephen Hemminger
> > > <sthemmin@microsoft.com>
> > > Subject: Re: [dpdk-dev] [PATCH v2] examples/client_server_mp: check
> > > port ownership
> > >
> > > On Sun, 7 Jul 2019 05:44:55 +0000
> > > Matan Azrad <matan@mellanox.com> wrote:
> > >
> > > > > +	for (count = 0; pm != 0; pm >>= 1, ++count) {
> > > > > +		struct rte_eth_dev_owner owner;
> > > > > +
> > > > > +		if ((pm & 0x1) == 0)
> > > > > +			continue;
> > > > > +
> > > > > +		if (count >= max_ports) {
> > > > > +			printf("WARNING: requested port %u not
> present -
> > > > > ignoring\n",
> > > > > +				count);
> > > > > +			continue;
> > > > > +		}
> > > > > +		if (rte_eth_dev_owner_get(count, &owner) < 0) {
> > > > > +			printf("ERROR: can not find port %u
> owner\n",
> > > > > count);
> > > >
> > > > What if some entity will take ownership later?
> > > > If you want the app will be ownership aware:
> > > > 	if you sure that you want this port to be owned by this
> > > > application
> > > you need to take ownership on it.
> > > > else:
> > > > the port is hidden by RTE_ETH_FOREACH_DEV if it is owned by some
> entity.
> > > > see how it was done in testpmd function: port_id_is_invalid().
> > >
> > > There are no mysterious entities in DPDK.
> > > The only thing that can happen later is hotplug, and that will not
> > > change state of existing port.
> > > This model is used for all applications.  The application does not
> > > take ownership, only device drivers do.
> >
> > A long discussions were done on it.
> > There is an application model to take ownership as I wrote you above.
> > You chose in the second option - not to be ownership aware.
> >
> > From docs:
> > "10.4.2. Port Ownership
> > The Ethernet devices ports can be owned by a single DPDK entity
> (application, library, PMD, process, etc). The ownership mechanism is
> controlled by ethdev APIs and allows to set/remove/get a port owner by
> DPDK entities. Allowing this should prevent any multiple management of
> Ethernet port by different entities.
> >
> > Note
> >
> > It is the DPDK entity responsibility to set the port owner before using it and
> to manage the port usage synchronization between different threads or
> processes."
> >
> > > The whole portmask as command-line parameter is a bad user
> > > experience now, but that is a different problem.
> >
> > I think, this is the problem you should solve here.
> 
> No other application is doing this: testpmd, l3fwd, ... why do you think this
> application is different. Plus you would be putting a new requirement on all
> the user applications. That would be a user hostile change.

As I said above:
Apps have 2 options:
1. be ownership aware and to take ownership on its ports.
2. not be ownership aware and use by RTE_ETH_FOREACH_DEV to detect the application ports.

Most of the apps should use the second option. (see testpmd).

Matan.