Re: [dpdk-dev] [PATCH v2] ethdev: add IPv4 checksum RSS offload type

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 6/3/21 11:03 AM, Alvin Zhang wrote:
> This patch defines new RSS offload type for IPv4 checksum,
> which is required when users want to distribute packets based
> on the IPv4 checksum field.
> 
> For example "flow create 0 ingress pattern eth / ipv4 / end
> actions rss types ipv4-chksum end queues end / end", this flow
> causes all matching packets to be distributed to queues on
> basis of IPv4 checksum.
> 
> Signed-off-by: Alvin Zhang <alvinx.zhang@intel.com>

The patch LGTM now. I hope we'll have a PMD in the release
cycle which supports it.

In fact it is a funny idea. Let's consider a TCP connection
and routing change with one extra hop on the way while
the connection is alive. Or a UDP stream in the same
conditions. If so, TTL will different, checksum changes and
connection packets may be delivered to a different Rx queue.
May be sometimes it is not important and/or can't happen.

L4 checksum sounds better from this point of view since
it covers IP addresses and transport ports and less bits
to hash. The only concern is distribution fairness, but
I keep the topic to those who understand corresponding
math better.

> ---
>  app/test-pmd/cmdline.c  | 2 ++
>  app/test-pmd/config.c   | 1 +
>  lib/ethdev/rte_ethdev.h | 1 +
>  3 files changed, 4 insertions(+)
> 
> diff --git a/app/test-pmd/cmdline.c b/app/test-pmd/cmdline.c
> index 0268b18..32da066 100644
> --- a/app/test-pmd/cmdline.c
> +++ b/app/test-pmd/cmdline.c
> @@ -2254,6 +2254,8 @@ struct cmd_config_rss {
>  		rss_conf.rss_hf = ETH_RSS_ECPRI;
>  	else if (!strcmp(res->value, "mpls"))
>  		rss_conf.rss_hf = ETH_RSS_MPLS;
> +	else if (!strcmp(res->value, "ipv4-chksum"))
> +		rss_conf.rss_hf = ETH_RSS_IPV4_CHKSUM;
>  	else if (!strcmp(res->value, "none"))
>  		rss_conf.rss_hf = 0;
>  	else if (!strcmp(res->value, "level-default")) {
> diff --git a/app/test-pmd/config.c b/app/test-pmd/config.c
> index 43c79b5..2c0c415 100644
> --- a/app/test-pmd/config.c
> +++ b/app/test-pmd/config.c
> @@ -140,6 +140,7 @@
>  	{ "gtpu", ETH_RSS_GTPU },
>  	{ "ecpri", ETH_RSS_ECPRI },
>  	{ "mpls", ETH_RSS_MPLS },
> +	{ "ipv4-chksum", ETH_RSS_IPV4_CHKSUM },
>  	{ NULL, 0 },
>  };
>  
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> index faf3bd9..f10d834 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -537,6 +537,7 @@ struct rte_eth_rss_conf {
>  #define ETH_RSS_PPPOE		   (1ULL << 31)
>  #define ETH_RSS_ECPRI		   (1ULL << 32)
>  #define ETH_RSS_MPLS		   (1ULL << 33)
> +#define ETH_RSS_IPV4_CHKSUM	   (1ULL << 34)
>  
>  /*
>   * We use the following macros to combine with above ETH_RSS_* for
>