Re: [dpdk-dev] [dpdk-stable] [PATCH v3 14/22] net/ena: indicate Rx RSS hash presence

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

On 5/6/2021 3:25 PM, Michal Krawczyk wrote:
> To make it possible to the app to determine if the hash was calculated
> for the packet or not, the PKT_RX_RSS_HASH should be set in the mbuf's
> ol_flags.
> 
> As the PMD wasn't setting that, the application couldn't check if there
> is a hash in a proper way.
> 
> The hash is valid only if it's UDP or TCP and the IP packet wasn't
> fragmented.
> 
> Fixes: e5df9f33db00 ("net/ena: fix passing RSS hash to mbuf")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Michal Krawczyk <mk@semihalf.com>
> Reviewed-by: Igor Chauskin <igorch@amazon.com>
> Reviewed-by: Amit Bernstein <amitbern@amazon.com>
> ---
>  drivers/net/ena/ena_ethdev.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ena/ena_ethdev.c b/drivers/net/ena/ena_ethdev.c
> index 6092288239..5d107775f4 100644
> --- a/drivers/net/ena/ena_ethdev.c
> +++ b/drivers/net/ena/ena_ethdev.c
> @@ -51,6 +51,8 @@
>  
>  #define ENA_MIN_RING_DESC	128
>  
> +#define ENA_PTYPE_HAS_HASH	(RTE_PTYPE_L4_TCP | RTE_PTYPE_L4_UDP)
> +
>  enum ethtool_stringset {
>  	ETH_SS_TEST             = 0,
>  	ETH_SS_STATS,
> @@ -314,6 +316,11 @@ static inline void ena_rx_mbuf_prepare(struct rte_mbuf *mbuf,
>  		else
>  			ol_flags |= PKT_RX_L4_CKSUM_GOOD;
>  
> +	if (likely((packet_type & ENA_PTYPE_HAS_HASH) && !ena_rx_ctx->frag)) {
> +		ol_flags |= PKT_RX_RSS_HASH;
> +		mbuf->hash.rss = ena_rx_ctx->hash;
> +	}

The driver should announce the 'DEV_RX_OFFLOAD_RSS_HASH' offload capability
first, and should set 'PKT_RX_RSS_HASH' only if application requests the
'DEV_RX_OFFLOAD_RSS_HASH'.


Normally this is an optimization to not always update the 'mbuf->hash.rss' but
wait for explicit request from application for it.

But there is no practical performance gain for some PMDs and they enable it even
user does not ask for it [1] (of course if RSS is enabled), if this is same for
'ena' you can do the same.

[1]
https://git.dpdk.org/dpdk/tree/drivers/net/ixgbe/ixgbe_ethdev.c?h=v21.05-rc2#n2384

> +
>  	mbuf->ol_flags = ol_flags;
>  	mbuf->packet_type = packet_type;
>  }
> @@ -2245,8 +2252,6 @@ static uint16_t eth_ena_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
>  			++rx_ring->rx_stats.bad_csum;
>  		}
>  
> -		mbuf->hash.rss = ena_rx_ctx.hash;
> -
>  		rx_pkts[completed] = mbuf;
>  		rx_ring->rx_stats.bytes += mbuf->pkt_len;
>  	}
>