Re: [PATCH v8 01/10] ethdev: overwrite some comment related to RSS

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

On 11/1/2023 7:40 AM, Jie Hai wrote:
> 1. overwrite the comments of fields of 'rte_eth_rss_conf'.
> 2. Add comments for RTE_ETH_HASH_FUNCTION_DEFAULT.
> 
> Signed-off-by: Jie Hai <haijie1@huawei.com>
> ---
>  lib/ethdev/rte_ethdev.h | 34 +++++++++++++++++++---------------
>  lib/ethdev/rte_flow.h   |  1 +
>  2 files changed, 20 insertions(+), 15 deletions(-)
> 
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> index a53dd5a1efec..343a134fdd12 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -448,24 +448,28 @@ struct rte_vlan_filter_conf {
>  /**
>   * A structure used to configure the Receive Side Scaling (RSS) feature
>   * of an Ethernet port.
> - * If not NULL, the *rss_key* pointer of the *rss_conf* structure points
> - * to an array holding the RSS key to use for hashing specific header
> - * fields of received packets. The length of this array should be indicated
> - * by *rss_key_len* below. Otherwise, a default random hash key is used by
> - * the device driver.
> - *
> - * The *rss_key_len* field of the *rss_conf* structure indicates the length
> - * in bytes of the array pointed by *rss_key*. To be compatible, this length
> - * will be checked in i40e only. Others assume 40 bytes to be used as before.
> - *
> - * The *rss_hf* field of the *rss_conf* structure indicates the different
> - * types of IPv4/IPv6 packets to which the RSS hashing must be applied.
> - * Supplying an *rss_hf* equal to zero disables the RSS feature.
>   */
>  struct rte_eth_rss_conf {
> -	uint8_t *rss_key;    /**< If not NULL, 40-byte hash key. */
> +	/**
> +	 * In rte_eth_dev_rss_hash_conf_get(), the *rss_key_len* should be
> +	 * greater than or equal to the *hash_key_size* which get from
> +	 * rte_eth_dev_info_get() API. And the *rss_key* should contain at least
> +	 * *hash_key_size* bytes. If not meet these requirements, the query
> +	 * result is unreliable even if the operation returns success.
> +	 *
> +	 * In rte_eth_dev_rss_hash_update() or rte_eth_dev_configure(), if
> +	 * *rss_key* is not NULL, the *rss_key_len* indicates the length of the
> +	 * *rss_key* in bytes of the array pointed by *rss_key*, 
>

I think it is sufficient to say "length of the *rss_key* in bytes".


>          and it should
> +	 * be equal to *hash_key_size*. 
>

I don't know if we missed something here, first driver reports key size
via 'rte_eth_dev_info_get()::hash_key_size', later other APIs require
'rss_key_len' parameter that should be same as 'hash_key_size', as
driver already know this parameter why we are requesting it back from
the application?


>>          Otherwise, drivers are free to use a
> +	 * random or a default key or to ignore this configuration.
> +	 */
>


I guess above clause describes when 'rss_key' is null, can you please
clarify it as following, perhaps with a line break:
"If *rss_key* is NULL, drivers are free to use a random or a default key."


For the "Drivers are free to ignore the *rss_key_len* and assume key
length is 40 bytes." part, as checks in ethdev layer now forces
application to provide 'rss_key_len' as 'hash_key_size', I think we can
remove above, as application will provide 40 bytes when it is the case.

My concern is this check now can break some applications, because
'rss_key_len' wasn't mandatory previously, but it became now.


Overall it becomes:
"
In rte_eth_dev_rss_hash_update() or rte_eth_dev_configure(), if
*rss_key* is not NULL, the *rss_key_len* indicates the length of the
*rss_key* in bytes and it should be equal to *hash_key_size*.
If *rss_key* is NULL, drivers are free to use a random or a default key.
"



> +	uint8_t *rss_key;
>  	uint8_t rss_key_len; /**< hash key length in bytes. */
> -	uint64_t rss_hf;     /**< Hash functions to apply - see below. */
> +	/**
> +	 * Indicates the type of packets or the specific part of packets to
> +	 * which RSS hashing is to be applied.
> +	 */
> +	uint64_t rss_hf;
>  };
>  
>  /*
> diff --git a/lib/ethdev/rte_flow.h b/lib/ethdev/rte_flow.h
> index c16fe8c21f2f..751c29a0f3f3 100644
> --- a/lib/ethdev/rte_flow.h
> +++ b/lib/ethdev/rte_flow.h
> @@ -3226,6 +3226,7 @@ struct rte_flow_query_count {
>   * Hash function types.
>   */
>  enum rte_eth_hash_function {
> +	/** DEFAULT means driver decides which hash algorithm to pick. */
>  	RTE_ETH_HASH_FUNCTION_DEFAULT = 0,
>  	RTE_ETH_HASH_FUNCTION_TOEPLITZ, /**< Toeplitz */
>  	RTE_ETH_HASH_FUNCTION_SIMPLE_XOR, /**< Simple XOR */