Re: [dpdk-dev] [PATCH v1] eal: add manual probing option

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, Oct 1, 2019 at 7:39 PM Gaëtan Rivet <gaetan.rivet@6wind.com> wrote:
>
> On Tue, Oct 01, 2019 at 03:19:42PM +0530, Jerin Jacob wrote:
> > On Tue, Oct 1, 2019 at 2:40 PM Gaėtan Rivet <gaetan.rivet@6wind.com> wrote:
> > >
> > > On Mon, Sep 30, 2019 at 11:53:33AM -0700, Stephen Hemminger wrote:
> > > > On Mon, 30 Sep 2019 14:51:03 +0200
> > > > Gaetan Rivet <gaetan.rivet@6wind.com> wrote:
> > > >
> > > > > Add a new EAL option enabling manual probing in the EAL.
> > > > > This command line option will configure the EAL so that buses
> > > > > will not trigger their probe step on their own.
> > > > >
> > > > > Applications are then expected to hotplug devices as they see fit.
> > > > >
> > > > > Devices declared on the command line by the user (using -w and --vdev),
> > > > > will be probed using the hotplug API, in the order they are declared.
> > > > >
> > > > > This has the effect of offering a way for users to control probe order
> > > > > of their devices, for drivers requiring it.
> > > > >
> > > > > Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
> > > >
> > > > I have no problems with the patch, but it would help if there was better
> > > > way to handle device naming policy in DPDK. Applications that depend on
> > > > particular port number are prone to get broken by changes in surrounding
> > > > OS or hardware environment. Just like Linux applications that are built
> > > > to depend on "eth0"; which is unfortunately all too common.
> > >
> > > Hello Stephen,
> > >
> > > This patch is a way to avoid having the PCI bus defining the probe order
> > > with the current hardware environment. It seems to be a step in the
> > > right direction for the issue you identify.
> > >
> > > There is a tight coupling between device names and driver matches for
> > > the vdev bus, but that seems difficult to avoid.
> > >
> > > Do you see other EAL APIs fostering an over reliance of downstream
> > > systems on device names?
> > >
> > > I pushed a few months back a way to iterate / match devices by their
> > > properties. If you identify other pain points, this could certainly be
> > > improved as well.
> >
> >
> > And this mode will be kicked in only when "--manual-probe" selected on
> > eal arguments.
> > So it won't change the behavior of the existing applications.
>
> If I read you correctly, if hardware independence is the proper way to function,
> we should switch entirely to it.
>
> I agree, but that means rewriting entirely the probe step of rte_bus.
> This patch is a incremental step, I preferred to keep risks low.

+1

>
> It is not clear from your remark whether you are considering this
> limitation a good or a bad thing however :)

I am considering it as a good step.

> Can you be a bit more explicit?
>
> --
> Gaėtan Rivet
> 6WIND