Re: [PATCH] ethdev: fix device init without socket-local memory

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 7/11/2024 1:35 PM, Bruce Richardson wrote:
> When allocating memory for an ethdev, the rte_malloc_socket call used
> only allocates memory on the NUMA node/socket local to the device. This
> means that even if the user wanted to, they could never use a remote NIC
> without also having memory on that NIC's socket.
> 
> For example, if we change examples/skeleton/basicfwd.c to have
> SOCKET_ID_ANY as the socket_id parameter for Rx and Tx rings, we should
> be able to run the app cross-numa e.g. as below, where the two PCI
> devices are on socket 1, and core 1 is on socket 0:
> 
>  ./build/examples/dpdk-skeleton -l 1 --legacy-mem --socket-mem=1024,0 \
> 		-a a8:00.0 -a b8:00.0
> 
> This fails however, with the error:
> 
>   ETHDEV: failed to allocate private data
>   PCI_BUS: Requested device 0000:a8:00.0 cannot be used
> 
> We can remove this restriction by doing a fallback call to general
> rte_malloc after a call to rte_malloc_socket fails. This should be safe
> to do because the later ethdev calls to setup Rx/Tx queues all take a
> socket_id parameter, which can be used by applications to enforce the
> requirement for local-only memory for a device, if so desired. [If
> device-local memory is present it will be used as before, while if not
> present the rte_eth_dev_configure call will now pass, but the subsequent
> queue setup calls requesting local memory will fail].
> 
> Fixes: e489007a411c ("ethdev: add generic create/destroy ethdev APIs")
> Fixes: dcd5c8112bc3 ("ethdev: add PCI driver helpers")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> Signed-off-by: Padraig Connolly <padraig.j.connolly@intel.com>
>

Hi Bruce,

If device-local memory is present, behavior will be same, so I agree
this is low impact.

But for the case device-local memory is NOT present, should we enforce
the HW setup is the question. This can be beneficial for users new to DPDK.

Probably 'dev_private' on its own has small impact on the performance
(although it may depend if these fields used in datapath), but it may be
vehicle to enforce local memory.

What is enabled by enabling app to run on cross-numa memory, since on a
production I expect users would like to use device-local memory for
performance reasons anyway?


Also I am not sure if this is a fix, or change of a intentional behavior.