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

Gaëtan Rivet gaetan.rivet at 6wind.com
Tue Oct 1 16:09:48 CEST 2019


On Tue, Oct 01, 2019 at 03:19:42PM +0530, Jerin Jacob wrote:
> On Tue, Oct 1, 2019 at 2:40 PM Gaëtan Rivet <gaetan.rivet at 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 at 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 at 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.

It is not clear from your remark whether you are considering this
limitation a good or a bad thing however :)
Can you be a bit more explicit?

-- 
Gaëtan Rivet
6WIND


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