Regarding port numbers assigned by DPDK for PCI devices

[Prashant Upadhyaya]

On Tue, 30 Jul 2024 at 13:45, Bruce Richardson <bruce.richardson at intel.com>
wrote:

> On Tue, Jul 30, 2024 at 11:06:56AM +0530, Prashant Upadhyaya wrote:
> >    On Mon, 29 Jul 2024 at 23:13, Dmitry Kozlyuk
> >    <[1]dmitry.kozliuk at gmail.com> wrote:
> >
> >      2024-07-29 22:18 (UTC+0530), Prashant Upadhyaya:
> >      > Hi,
> >      >
> >      > I have 4 ethernet interfaces available as PCI devices.
> >      > The PCI addresses are known.
> >      > When I start my DPDK application, it starts up properly and
> >      assigns the
> >      > port numbers to them as 0, 1, 2, 3 expectedly.
> >      >
> >      > However, is there a way I can force that a particular PCI address
> >      should be
> >      > identified as port 0 by DPDK, another one as port 1 and so forth ?
> >      > Does passing the arguments like -a <address1> -a <address2> to
> >      rte_eal_init
> >      > ensure that, or is there any other way, or is there no way ?
> >      >
> >      > I am on 24.03
> >      >
> >      > Regards
> >      > -Prashant
> >      Hi,
> >      Why do you need specific port numbers assigned to devices?
> >      If you're going to use devices for different purposes,
> >      you'd better have an application-level configuration
> >      to specify PCI addresses to use for each purpose.
> >      Iterate devices to match the address and find the port number.
> >      It is also possible to disable automatic probing with "-a 0:0.0",
> >      then to use rte_dev_probe() + rte_dev_event_callback_register()
> >      to add devices and to get their port numbers.
> >      However, this API, strictly speaking, does not guarantee
> >      that the numbers will be assigned sequentially.
> >      One advantage of using hot-plug is that you can build devargs
> >      from within the application (or from configuration).
> >      Refer to "rte_dev.h" in any case.
> >      Multiple "-a" don't work the way you've described.
> >
> >    Thanks Dmitry. Ok, so if I have the port number with me, and I know it
> >    corresponds to a PCI device, how do I find out the PCI address of this
> >    device corresponding to this port number. I believe I can
> >    do rte_eth_dev_info_get to get the struct rte_eth_dev_info and from
> >    there the rte_device, but what after that ? I saw some references
> >    to RTE_DEV_TO_PCI but that macro isn't available for compilation after
> >    DPDK is installed as it is an internal header file and thus not a
> macro
> >    for application usage and wouldn't compile at application level.
> >    Regards
> >    -Prashant
> >
> The PCI device id is used as the device name in that case so rte_dev_name
> should get you what you want.
>
> I'd also +1 the suggestion of having your app hotplug in the devices
> post-init, if you want specific devices to have specific ids. Although it
> is not guaranteed, DPDK does currently assign the ids sequentially. I've
> used this approach myself in the past in some test apps where I wanted
> ports in a particular sequence.
>
> /Bruce
>

Thanks Bruce, makes sense.

Regards
-Prashant
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