Re: [dpdk-dev] [PATCH 3/7] ethdev: add flow action type update as an offload

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 8/18/19 7:59 AM, Shahaf Shuler wrote:
> Friday, August 16, 2019 11:05 AM, Andrew Rybchenko:
>> <marko.kovacevic@intel.com>; Thomas Monjalon <thomas@monjalon.net>
>> Cc: dev@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH 3/7] ethdev: add flow action type update as
>> an offload
>>
>> On 8/16/19 8:55 AM, pbhagavatula@marvell.com wrote:
>>> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>>
>>> Add new Rx offload flag `DEV_RX_OFFLOAD_FLOW_MARK` that can be
>> used to
>>> enable/disable PMDs write to `rte_mbuf::hash::fdir::hi`.
>> Notes similar to RSS hash.
>>
>> It requires better motivation why. It lets Rx queue know that it will be used
>> as flow action MARK target and the queue should be configured to deliver
>> the mark from NIC to PMD and processed in the driver.
> This one is even worse than the RSS (sorry).
>
> First - the API breakage exists also here and if we want to include such patch we should have proper doc on RN.

Yes, there is a deprecation notice for it in v19.08 and I already
mentioned in review notes for the patch [1/7] that release notes
are required.

> Second - the user explicitly inserted a rte_flow rule w/ action mark. Its expectation is to receive his mark on the mbuf (otherwise why would it set this action?).  it is not expected from the user to set another offload flag just to enable the mark set on the mbuf. It makes the user experience very convoluted.
> Third - so far we never reported rte_flow capabilities, and there is a good reason for it - the cap matrix is too big. For rte_flow the chosen approach was trail and error. If we start w/ the flow mark, the amount of cap bits the application will need to monitor will be huge.

The feature differs a lot from other rte_flow features since it
adds Rx meta information.
And yes, rte_flow rule to set mark should fail with appropriate
diagnostics if the offload is supported by not enabled or not
supported at all. So, application will be informed and I think
it is less worse than RSS hash.

> My suggestion here, for PMD that wants to optimize their datapath is to check if flow w/ mark action was inserted on the queue. So long there is no such flow they can disable the set of the mark.

Unfortunately the information is required on Rx queue setup
stage and rte_rule insertion is too late.

Anyway, the important point here is all Rx offloads consistency:
want something - enable it. The only remaining exception is
packet type which default behaviour is preserved since really
flexible solution suggested by Konstantin.

>> Also I think that flow API action MARK documentation should be updated to
>> mentioned the offload.
>>
>>> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>> ---
>>>    doc/guides/nics/features.rst   | 12 ++++++++++++
>>>    lib/librte_ethdev/rte_ethdev.h |  1 +
>>>    2 files changed, 13 insertions(+)
>>>
>>> diff --git a/doc/guides/nics/features.rst
>>> b/doc/guides/nics/features.rst index f79b69b38..d67430d90 100644
>>> --- a/doc/guides/nics/features.rst
>>> +++ b/doc/guides/nics/features.rst
>>> @@ -594,6 +594,18 @@ application to set ptypes it is interested in.
>>>    * **[provides]   mbuf**: ``mbuf.packet_type``.
>>>
>>>
>>> +.. _nic_features_flow_action_type_update:
>> May be  _nic_features_flow_mark ?
>>
>>> +
>>> +Flow type update
>> May be "Flow mark delivery" ?
>>
>>> +----------------
>>> +
>>> +Supports flow action type update to ``mbuf.ol_flags`` and
>> ``mbuf.hash.fdir.hi``.
>>> +
>>> +* **[uses]     rte_eth_rxconf,rte_eth_rxmode**:
>> ``offloads:DEV_RX_OFFLOAD_FLOW_TYPE``.
>>
>> DEV_RX_OFFLOAD_FLOW_MARK, not TYPE.
>>
>>
>>
>>> +* **[provides] mbuf**: ``mbuf.ol_flags:PKT_RX_FDIR``,
>>> +``mbuf.ol_flags:PKT_RX_FDIR_ID;``,
>>> +  ``mbuf.hash.fdir.hi``
>>> +
>>> +
>>>    .. _nic_features_timesync:
>>>
>>>    Timesync
>>> diff --git a/lib/librte_ethdev/rte_ethdev.h
>>> b/lib/librte_ethdev/rte_ethdev.h index 889486a11..4a0cff830 100644
>>> --- a/lib/librte_ethdev/rte_ethdev.h
>>> +++ b/lib/librte_ethdev/rte_ethdev.h
>>> @@ -1014,6 +1014,7 @@ struct rte_eth_conf {
>>>    #define DEV_RX_OFFLOAD_SCTP_CKSUM	0x00020000
>>>    #define DEV_RX_OFFLOAD_OUTER_UDP_CKSUM  0x00040000
>>>    #define DEV_RX_OFFLOAD_RSS_HASH		0x00080000
>>> +#define DEV_RX_OFFLOAD_FLOW_MARK	0x00100000
>>>
>>>    #define DEV_RX_OFFLOAD_CHECKSUM
>> (DEV_RX_OFFLOAD_IPV4_CKSUM | \
>>>    				 DEV_RX_OFFLOAD_UDP_CKSUM | \
>> Add to rte_rx_offload_names