[PATCH v4 1/7] ethdev: recomment some definitions related to RSS

[Jie Hai]

On 2023/9/21 0:39, Ferruh Yigit wrote:
> On 9/8/2023 9:00 AM, Jie Hai wrote:
>> 1. Recomment fields of 'rte_eth_rss_conf'.
>> 2. Add comments for RTE_ETH_HASH_FUNCTION_DEFAULT.
>>
>> Signed-off-by: Jie Hai <haijie1 at huawei.com>
>> ---
>>   lib/ethdev/rte_ethdev.h | 28 +++++++++++++---------------
>>   lib/ethdev/rte_flow.h   |  4 ++++
>>   2 files changed, 17 insertions(+), 15 deletions(-)
>>
>> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
>> index 04a2564f222a..40cfbb7efddd 100644
>> --- a/lib/ethdev/rte_ethdev.h
>> +++ b/lib/ethdev/rte_ethdev.h
>> @@ -448,24 +448,22 @@ 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. */
>> +	/**
>> +	 * If not NULL, 40-byte hash key to use for hashing specific header
>> +	 * fields of received packets. The size of rss_key should be indicated
>> +	 * by *rss_key_len* below.
>>
> 
> It says key length is 40 bytes, also says key length is defined by
> 'rss_key_len'. I wonder how can we clarify this more, what about like:
> 
> If not NULL, hash key to use for hashing.
> The size of rss_key should be indicated by *rss_key_len* below. Drivers
> are free to ignore the *rss_key_len* and assume key length is 40 bytes.
> 
Not all drivers use 40-bytes hash key,
e.g. the cnxk driver use hash key with length ROC_NIX_RSS_KEY_LEN(48).
I think it's best not to mention '40 bytes' in the comments.

This structure is used for querying and configuring, How about the 
following statements:

	/**
	 * If used to query, the'rss_key_len' indicates the sizeof rss key of
	 * the hardware. And only when rss_key_len is not zero, the 'rss_key'
	 * is valid.
	 * If used to configure, rss_key_len indicates the length of the
	 * 'rss_key' if 'rss_key' is not empty.
	 */
> 
>> +	 * Otherwise, a default random hash key is used by the device driver.
>> +	 */
>> +	uint8_t *rss_key;
>>   	uint8_t rss_key_len; /**< hash key length in bytes. */
>> -	uint64_t rss_hf;     /**< Hash functions to apply - see below. */
>> +	/**
>> +	 * The different types of packets to which the RSS hashing must be
>> +	 * applied, may be combined with SRC/DST_ONLY, see below.
> 
> I find this difficult to understand, can we simplify it?
> 
> The name 'hf' (hash function) is confusing on its own, but it is too
> much burden to update it, at least we can clarify it with the above
> documentation.
> 
> rte_flow defines it as 'types' (rte_flow_action_rss.type)
> (and it has 'func' for "hash algorithm" to increase confusion).
> 
> Can we define something like (please don't use as it is, just thinking):
> "
> Set part of the packet that hashing will be applied for RSS purposes
> (see RTE_ETH_RSS_*).
How about "Indicating which type of packets and which part of the 
packets to be applied for RSS hash, (see RTE_ETH_RSS_*)."
> "
> 
>> +	 * Supplying an *rss_hf* equal to zero disables the RSS feature.
>> +	 */
> 
> s/Supply/Set/ ?
> "Setting *rss_hf* to zero disables the RSS feature."
Will correct.
> 
>> +	uint64_t rss_hf;
>>   };
>>   
>>   /*
>> diff --git a/lib/ethdev/rte_flow.h b/lib/ethdev/rte_flow.h
>> index 2ebb76dbc083..3bd0dc64fbe2 100644
>> --- a/lib/ethdev/rte_flow.h
>> +++ b/lib/ethdev/rte_flow.h
>> @@ -3187,6 +3187,10 @@ struct rte_flow_query_count {
>>    * Hash function types.
>>    */
>>   enum rte_eth_hash_function {
>> +	/**
>> +	 * DEFAULT means that conformance to a specific hash algorithm is
>> +	 * uncared to the caller. The driver can pick the one it deems optimal.
> 
> Not sure about word 'uncared' usage here, what about:
> 
> "
> DEFAULT means driver decides which hash algorithm to pick.
> "
> 
That's better.
> 
> .