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

[Leon Romanovsky <leonro@nvidia.com>]

On Mon, Nov 09, 2020 at 03:52:29PM +0200, Gal Pressman wrote:
> On 09/11/2020 15:02, Leon Romanovsky wrote:
> > On Mon, Nov 09, 2020 at 02:47:07PM +0200, Gal Pressman wrote:
> >> On 09/11/2020 14:32, Leon Romanovsky wrote:
> >>> On Mon, Nov 09, 2020 at 02:27:16PM +0200, Gal Pressman wrote:
> >>>> On 09/11/2020 13:55, Leon Romanovsky wrote:
> >>>>> 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.
> >>>>
> >>>> For example, in an instance with multiple NICs and GPUs, it's common to examine
> >>>> the devices topology and distances, device bdfs are needed for that.
> >>>>
> >>>> Also, when analyzing dmesg logs the prints contain the ibdev name, which is not
> >>>> always enough when trying to debug the corresponding physical device.
> >>>
> >>> Gal,
> >>>
> >>> I'm asking which problem will solve new nldev and not why BDF is important. :)
> >>
> >> This patch follows the implementation of other fields in fill_dev_info() such as
> >> port index, fw version, node guid, sys image guid, node type, dev protocol, etc,
> >> which also exist in sysfs.
> >>
> >> You added most of these new nldevs not long ago, so I find your question a bit
> >> confusing.. Can you please explain your concerns and why you think bdf is different?
> >
> > Almost all fields that you mentioned were needed to implement rdma_rename
> > utility that followed systemd internal implementation and/or were used in
> > the rdma-core.
> >
> > The FW version is clearly an exemption to the above.
> >
> > So I'm trying to understand the rationale behind BDF and how it will
> > work with different bus variants that we will have. Like Parav said,
> > the IB is connected to auxiliary bus (no BDF) and will have parent
> > with BDF too at the same time.
>
> We can review the different cases and make sure it works as expected (and what's
> expected), but let's first reach an agreement if I should continue with this
> work or not.

I don't know.

Thanks