Re: [PATCH for-next] RDMA/nldev: Add parent bdf to device information dump

[Leon Romanovsky <leonro@nvidia.com>]

On Mon, Nov 09, 2020 at 11:03:25AM +0200, Gal Pressman wrote:
>
> On 09/11/2020 7:09, Leon Romanovsky wrote:
> > On Sun, Nov 08, 2020 at 07:49:35PM -0400, Jason Gunthorpe wrote:
> >> On Sun, Nov 08, 2020 at 03:03:45PM +0200, Gal Pressman wrote:
> >>> On 05/11/2020 22:00, Jason Gunthorpe wrote:
> >>>> On Tue, Nov 03, 2020 at 05:45:26PM +0200, Gal Pressman wrote:
> >>>>> On 03/11/2020 16:22, Jason Gunthorpe wrote:
> >>>>>> On Tue, Nov 03, 2020 at 04:11:19PM +0200, Gal Pressman wrote:
> >>>>>>> On 03/11/2020 15:57, Leon Romanovsky wrote:
> >>>>>>>> On Tue, Nov 03, 2020 at 09:45:22AM -0400, Jason Gunthorpe wrote:
> >>>>>>>>> On Tue, Nov 03, 2020 at 03:26:27PM +0200, Gal Pressman wrote:
> >>>>>>>>>> Add the ability to query the device's bdf through rdma tool netlink
> >>>>>>>>>> command (in addition to the sysfs infra).
> >>>>>>>>>>
> >>>>>>>>>> In case of virtual devices (rxe/siw), the netdev bdf will be shown.
> >>>>>>>>>
> >>>>>>>>> Why? What is the use case?
> >>>>>>>>
> >>>>>>>> Right, and why isn't netdev (RDMA_NLDEV_ATTR_NDEV_NAME) enough?
> >>>>>>>
> >>>>>>> When taking system topology into consideration you need some way to pair the
> >>>>>>> ibdev and bdf, especially when working with multiple devices.
> >>>>>>> The netdev name doesn't exist on devices with no netdevs (IB, EFA).
> >>>>>>
> >>>>>> You are supposed to use sysfs
> >>>>>>
> >>>>>> /sys/class/infiniband/ibp0s9/device
> >>>>>>
> >>>>>> Should always be the physical device
> >>>>>>
> >>>>>>> Why rdma tool? Because it's more intuitive than sysfs.
> >>>>>>
> >>>>>> But we generally don't put this information into netlink BDF is just
> >>>>>> the start, you need all the other topology information to make sense
> >>>>>> of it, and all that is in sysfs only already
> >>>>>
> >>>>> As the commit message says, it's in addition to the device sysfs.
> >>>>>
> >>>>> Many (if not most) of the existing rdma netlink commands are duplicates of some
> >>>>> sysfs entries, but show it in a more "modern" way.
> >>>>> I'm not convinced that bdf should be treated differently.
> >>>>
> >>>> Why did you call it BDF anyhow? it has nothing to do with PCI BDF
> >>>> other than it happens to be the PDF for PCI devices. Netdev called
> >>>> this bus_info
> >>>
> >>> Are there non pci devices in the subsystem?
> >>
> >> Yes, HNS uses non-pci devices
> >>
> >>> I can rename to a more fitting name, will change to bus_info unless
> >>> someone has a better idea.
> >>
> >> The thing is, is is still useless. You have to consult sysfs to
> >> understand what bus it is scoped on to do anything further with
> >> it. Can't just assume it is PCI.
> >
> > Can anyone please remind me why are we doing it?
> > What problem do you solve here by adding new nldev attributes?
>
> https://lore.kernel.org/linux-rdma/0825e1bf-f913-d2c1-ad3f-35ba3d6b75ef@amazon.com/

Thanks, but IMHO it doesn't answer on the question about the problem.