[dpdk-users] MLX5: Using packet send scheduling / packet pacing

[Carsten Andrich <carsten.andrich@tu-ilmenau.de>]

Hello everyone,

I'm trying to use packet send scheduling [1] with DPDK 20.11 and the 
MLX5 PMD (NIC: ConnectX-5 MCX516A-CDAT). This patch contains some 
additional information on this feature also know as packet pacing [2].

According to MLX5's docs, packet pacing requires the "tx_pp" parameter 
[3, CTRL+F: "tx_pp"]. However, when firing up testpmd with that 
parameter, it fails as follows:

> # dpdk-testpmd -a 81:00.0,tx_pp=500 -- -i
> ...
> EAL: Probe PCI driver: mlx5_pci (15b3:1019) device: 0000:81:00.0 (socket 0)
> mlx5_pci: WQE rate mode is required for packet pacing
> mlx5_pci: probe of PCI device 0000:81:00.0 aborted after encountering an error: No such device
> common_mlx5: Failed to load driver = mlx5_pci.
>
> EAL: Requested device 0000:81:00.0 cannot be used
The error message originates here [4] and is caused by what to me 
appears to be a value read from the NIC [5]. Unfortunately, that leaves 
me clueless on how to activate the required "WQE rate mode".  According 
to the output of ibv_devinfo, my NIC does support packet pacing:

> # ibv_devinfo -v 81:00.0
> ...
> 	packet_pacing_caps:
> 		qp_rate_limit_min:	1kbps
> 		qp_rate_limit_max:	100000000kbps
> 		supported_qp:
> 					SUPPORT_RAW_PACKET
I'd be grateful for any information on how to get packet pacing up and 
running. Am I just missing another required option (which is not given 
in the docs) or does my NIC lack packet pacing support?

Thank you very much in advance.

Best regards,
Carsten

[1] 
https://doc.dpdk.org/api/rte__ethdev_8h.html#a990d8351447a710628cbb24a28d3252d
[2] https://patches.dpdk.org/patch/73742/
[3] https://doc.dpdk.org/guides/nics/mlx5.html#run-time-configuration
[4] 
http://code.dpdk.org/dpdk/v20.11/source/drivers/net/mlx5/linux/mlx5_os.c#L1278
[5] 
http://code.dpdk.org/dpdk/v20.11/source/drivers/common/mlx5/mlx5_devx_cmds.c#L748