RSS for ENA

[Stephen Hemminger]

On Sun, 11 Aug 2024 19:55:08 +0400 (+04)
Ivan Malov <ivan.malov at arknetworks.am> wrote:

> Hi Fabio,
> 
> Have you considered to select MQ mode 'RSS' [1] via 'dev_conf.rxmode.mq_mode'
> during 'rte_eth_dev_configure' [2] stage? Just to double-check.
> 
> Also, the 'RSS_HASH' flag could possibly mean the availability of 32-bit hash
> value in received mbufs rather than support for RSS distribution as a whole.
> 
> [1] https://doc.dpdk.org/api-24.07/rte__ethdev_8h.html#a586b8e86131b4ec0ccaf464e847ccf3e
> [2] https://doc.dpdk.org/api-24.07/rte__ethdev_8h.html#a1a7d3a20b102fee222541fda50fd87bd

Please do not top post on mailing lists.

> Hi,
> I'm a bit puzzled why DPDK is reporting RSS to be not available on my ENA port (at AWS) when I'm expecting it to be.
> 
> My setup is:
>       c7a.4xlarge
>     [ENA_COM: ena_com_validate_version]ENA device version: 0.10
>     [ENA_COM: ena_com_validate_version]ENA controller version: 0.0.1 implementation version 1
> 16-cores (hyper-threading disabled),
> 4 ENA interfaces/network adapters, but only one (with public IP) is bound to igb_uio
> DPDK 24.07
> 6.5.0-1020-aws,
> Ubuntu 22.04.4 LTS,
> 
> 
> The device reports that 8 queues are available, but rte_eth_dev_info::rx_offload_capa does not have RTE_ETH_RX_OFFLOAD_RSS_HASH set after calling rte_eth_dev_info_get().
> 
> The flag value seems to be coming from here,
> https://github.com/DPDK/dpdk/blob/b3485f4293997d35b6daecc3437bb0c183a51fb3/drivers/net/ena/ena_ethdev.c#L2402
> Where the offload mask is:
>           (ena_com_dev_get_features_ctx*) get_feat_ctx->offload
>             tx = 3
>             rx_supported = 7
>             rx_enabled = 0
> 
> 
> Isn't RSS supposed to be available on this ENA setup?
> 
> If not, how am I supposed to distribute inbound packets across those 8 receive queues/CPUs?
> 
> Some notes, log:
>       at eth_ena_dev_init(), ena_use_large_llq_hdr() returned true
> ena_get_metrics_entries(): 0x6 customer metrics are supported
> ena_use_large_llq_hdr(): Recommended device entry size policy 4
> eth_ena_dev_init(): LLQ entry size 256B
> eth_ena_dev_init(): Placement policy: Low latency
> 

Yes, the OFFLOAD_RSS_HASH flag indicates that the received mbuf will contain the hash value.
This driver only does it if multi-queue is enabled (which makes sense).


You need rxmode.mq_mode with RTE_ETH_MQ_RX_RSS_FLAG to make use of all 8 queues.