Re: [PATCH v8] ethdev: add optimization hints in flow template table

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

On 2/2/2023 11:33 AM, Thomas Monjalon wrote:
> 02/02/2023 12:19, Rongwei Liu:
>> In case flow rules match only one kind of traffic in a flow table,
>> then optimization can be done via allocation of this table.
>> Such optimization is possible only if the application gives a hint
>> about its usage of the table during initial configuration.
>>
>> The transfer domain rules may process traffic from wire or vport,
>> which may correspond to two kinds of underlayer resources.
>> That's why the first two hints introduced in this patch are about
>> wire and vport traffic specialization.
>> Wire means traffic arrives from the uplink port while vport means
>> traffic initiated from VF/SF.
>>
>> There are two possible approaches for providing the hints.
>> Using IPv4 as an example:
>> 1. Use pattern item in both flow template table and rules.
>>
>>    template table 3 =
>>      transfer pattern ANY_VPORT / eth / ipv4 src is 255.255.255.255 / end
>>    flow rule =
>>      template_table 3 pattern ANY_VPORT / eth / ipv4 src is 1.1.1.1 / end
>>
>>    The pattern template 3 will be used only to match flows coming from
>>    vports.
>>    ANY_VPORT needs to be present in each flow rule.
>>    ANY_VPORT matching is redundant with IP src 1.1.1.1 because
>>    the user knows 1.1.1.1 is the IP of a vport.
>>
>> 2. Add specialization flag into flow template table attribute:
>>
>>    template table 3 =
>>      transfer VPORT_ORIG pattern eth / ipv4 src is 255.255.255.255 / end
>>    flow rule =
>>      template_table 3 pattern eth / ipv4 src is 1.1.1.1 / end
>>
>>    The pattern template 3 can be used only to match flows coming
>>    from vports.
>>
>> Approach 1 needs to specify the hint in each flow rule that wastes
>> memory and is not user friendly.
>> This patch takes the 2nd approach and introduces one new member
>> "specialize" into rte_flow_table_attr to indicate possible flow table
>> optimization.
>>
>> By default, there is no hint, so nothing change.
>> There is no guarantee that the hints will be effective in the driver.
>> The application functionality must not rely on the hints.
>>
>> Signed-off-by: Rongwei Liu <rongweil@nvidia.com>
>> Acked-by: Ori Kam <orika@nvidia.com>
> 
> Andrew gave this recent comment on v7:
> "
> Anyway, hint itself is OK and makes sense. Hopefully
> documentation highlights that pattern match is required.
> If so,
> 
> Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> "
> 
> Given the lines below, I assume the documentation is OK.
> 
>> +This attribute is not mandatory for driver to implement.
>> +If a hint is not supported, it will be silently ignored,
>> +and no special optimization is done.
>> +
>> +If a table is specialized, the application should make sure the rules
>> +comply with the table attribute.
>> +The application functionality must not rely on the hints,
>> +they are not replacing the matching criteria of flow rules.
> [...]
>> +/**@{@name Flags for template table attribute.
>> + * Each bit is an optional hint for table specialization,
>> + * offering a potential optimization at driver layer.
>> + * The driver can ignore the hints silently.
>> + * The hints do not replace any matching criteria.
>> + */
>> +/**
>> + * Specialize table for transfer flows which come only from wire.
>> + * It allows PMD not to allocate resources for non-wire originated traffic.
>> + * This bit is not a matching criteria, just an optimization hint.
>> + * Flow rules which match non-wire originated traffic will be missed
>> + * if the hint is supported.
>> + */
>> +#define RTE_FLOW_TABLE_SPECIALIZE_TRANSFER_WIRE_ORIG RTE_BIT32(0)
>> +/**
>> + * Specialize table for transfer flows which come only from vport (e.g. VF, SF).
>> + * It allows PMD not to allocate resources for non-vport originated traffic.
>> + * This bit is not a matching criteria, just an optimization hint.
>> + * Flow rules which match non-vport originated traffic will be missed
>> + * if the hint is supported.
>> + */
>> +#define RTE_FLOW_TABLE_SPECIALIZE_TRANSFER_VPORT_ORIG RTE_BIT32(1)
>> +/**@}*/
> [...]
>> +	/**
>> +	 * Optional hint flags for driver optimization.
>> +	 * The effect may vary in the different drivers.
>> +	 * The functionality must not rely on the hints.
>> +	 * Value is composed with RTE_FLOW_TABLE_SPECIALIZE_* based on application
>> +	 * design choices.
>> +	 * Misused hints may mislead the driver, it may result in an undefined behavior.
>> +	 */
>> +	uint32_t specialize;
> 
> Acked-by: Thomas Monjalon <thomas@monjalon.net>
> 


Applied to dpdk-next-net/main, thanks.