Re: [PATCH v4 2/3] ethdev: add standby state for live migration

[Thomas Monjalon <thomas@monjalon.net>]

01/02/2023 09:40, Jerin Jacob:
> On Wed, Feb 1, 2023 at 1:02 PM Andrew Rybchenko
> <andrew.rybchenko@oktetlabs.ru> wrote:
> >
> > On 2/1/23 01:55, Thomas Monjalon wrote:
> > > 31/01/2023 19:14, Jerin Jacob:
> > >> On Wed, Jan 18, 2023 at 9:15 PM Rongwei Liu <rongweil@nvidia.com> wrote:
> > >>>
> > >>> When a DPDK application must be upgraded,
> > >>> the traffic downtime should be shortened as much as possible.
> > >>> During the migration time, the old application may stay alive
> > >>> while the new application is starting and being configured.
> > >>>
> > >>> In order to optimize the switch to the new application,
> > >>> the old application may need to be aware of the presence
> > >>> of the new application being prepared.
> > >>> This is achieved with a new API allowing the user to change the
> > >>> new application state to standby and active later.
> > >>>
> > >>> The added function is trying to apply the new state to all probed
> > >>> ethdev ports. To make this API simple and easy to use,
> > >>> the same flags have to be accepted by all devices.
> > >>>
> > >>> This is the scenario of operations in the old and new applications:
> > >>> .       device: already configured by the old application
> > >>> .       new:    start as active
> > >>> .       new:    probe the same device
> > >>
> > >> How to probe same device if is already bind to another application?
> > >> vfio-pci wont allow this.
> > >
> > > I missed that part.
> > > There is no way to share a VFIO device between 2 applications?
> >
> > As I understand multi-process shares an VFIO device between
> > many application. As far as I remember it is just required to
> > pass corresponding file descriptor to another application.
> 
> I think, Here, it is two different primary application.

Yes it is 2 primary applications.

> Even if it is primary-secondary kind of case, bus or pci driver layer
> needs fixup,
> Currently, if we add allow list same PCI device on primary and secondary,
> the second app start will fail.

Can we imagine passing a VFIO handle to the new application?