[dpdk-dev] [PATCH v12 0/7] ethdev: add new Rx offload flags

[Andrew Rybchenko]

Hi Ferruh,

since I've reviewed I'll reply as I understand it.

On 10/17/19 8:43 PM, Ferruh Yigit wrote:
> On 10/17/2019 1:02 PM, pbhagavatula at marvell.com wrote:
>> From: Pavan Nikhilesh <pbhagavatula at marvell.com>
>>
>>   Add new Rx offload flags `DEV_RX_OFFLOAD_RSS_HASH` and
>>   `DEV_RX_OFFLOAD_FLOW_MARK`. These flags can be used to
>>   enable/disable PMD writes to rte_mbuf fields `hash.rss` and `hash.fdir.hi`
>>   and also `ol_flags:PKT_RX_RSS` and `ol_flags:PKT_RX_FDIR`.
> Hi Pavan,
>
> Initially sorry for involving late,
>
> When we expose an interface to the applications, they will expect those will be
> respected by underlying PMDs.
> As far as I can see drivers are updated to report new added Rx offload flags as
> supported capabilities but drivers are not using those flags at all, so
> application providing that flag won't really enable/disable anything, I think
> this is a problem and it is wrong to lie even for the PMDs J

It is required to let applications know that the offload is supported.
There are a number of cases when an offload cannot be disabled,
but it does not mean that the offload must not be advertised.
If driver see benefits from disabling the offload (e.g. avoid delivery
of RSS hash from NIC to host), it can do it after the patchset.

> Specific to `DEV_RX_OFFLOAD_RSS_HASH`, we have already some RSS config
> structures and it is part of the 'rte_eth_dev_configure()' API, won't it create
> multiple way to do same thing?

No, a new offload is responsible for RSS hash delivery from NIC to host
and fill in in mbuf returned to application on Rx.

> And for the `ol_flags:PKT_RX_RSS` flag, it was already used to mark that
> 'mbuf::hash::rss' is valid, right? Is there anything new related that in the set?

As I understand you mean, ol_flags::PKT_RX_RSS_HASH.
Yes, the new offload allows say if application needs it or now.
Basically it decouples RSS distribution and hash delivery.

> Specific to the `DEV_RX_OFFLOAD_FLOW_MARK` and `RTE_FLOW_ACTION_FLAG`, they are
> rte_flow actions, application can verify and later request these actions via
> rte_flow APIs. Why we are adding an additional RX_OFFLOAD flag for them?

The reason is basically the same as above. HW needs to know in advance,
if application is going to use flow marks and configure Rx queue to enable
the information delivery.

>>   Add new packet type set function `rte_eth_dev_set_supported_ptypes`,
>>   allows application to inform PMDs about the packet types it is interested
>>   in. Based on ptypes requested by application PMDs can optimize the Rx path.
> OK to the API, but why "Packet type parsing" feature updated to say it should
> implement this API?
> Is this API really required to say "Packet type parsing" supported by PMD?

As I understand it is not strictly required, but related to the feature.

>>   For example, if a given PMD doesn't support any packet types that the
>>   application is interested in then the application can disable[1] writes to
>>   `mbuf.packet_type` done by the PMD and use a software ptype parser.
>>        [1] rte_eth_dev_set_supported_ptypes(*port_id*, RTE_PTYPE_UNKNOWN,
>> 					  NULL, 0);
> And for the 7/7 patch, why we are updating all examples, is the API something do
> we really need to call for any DPDK application? I am for leaving the default
> behavior unless there is a very specific case for set or disable packet typing.
> Instead implement a command in testpmd to test this feature.

If an application does not use packet types provided in mbuf, it is
better to inform PMD that the information is not required to allow PMD
to do optimizations. Yes, may be it would be better to have it as the
default behaviour, but it would be behaviour change in comparison
to previous DPDK releases and it is better to avoid it.

Thanks,
Andrew.

>> v12 Changes:
>> -----------
>> - Rebase onto next-net.
>>
>> v11 Changes:
>> -----------
>> - Use RTE_DIM to get array size.
>> - Since we are using a list of MASKs to validate ptype_mask return -EINVAL
>>    if any unknown mask is set.
>> - Rebase to TOT.
>>
>> v10 Changes:
>> -----------
>> - Modify ptype_mask validation in set_supported_ptypes.(Andrew)
>>
>> v9 Changes:
>> ----------
>> - Add ptype_mask validation in set_supported_ptypes.(Andrew)
>> - Make description more verbose.
>>
>> v8 Changes:
>> ----------
>> - Make description more verbose.
>> - Set RTE_PTYPE_UNKNOWN in set_ptypes array when either get ot set ptypes
>>    is not supported by ethernet device.
>>
>> v7 Changes:
>> ----------
>> - Fix unused variable in net/octeontx2
>>
>> v6 Changes:
>> ----------
>> - Add additional checks for set supported ptypes.(Andrew)
>> - Clarify `rte_eth_dev_set_supported_ptypes` documentation.
>> - Remove DEV_RX_OFFLOAD_FLOW_MARK emulation from net/octeontx2.
>>
>> v5 Changes:
>> ----------
>> - Fix typos.
>>
>> v4 Changes:
>> ----------
>> - Set the last element in set_ptype array as RTE_PTYPE_UNKNOWN to mark the end
>>    of array.
>> - Fix invalid set ptype function call in examples.
>> - Remove setting rte_eth_dev_set_supported_ptypes to UNKNOWN in l3fwd-power.
>>
>> v3 Changes:
>> ----------
>> - Add missing release notes. (Andrew)
>> - Re-word various descriptions.
>> - Fix ptype set logic.
>>
>> v2 Changes:
>> ----------
>> - Update release notes. (Andrew)
>> - Redo commit logs. (Andrew)
>> - Disable ptype parsing for unsupported examples. (Jerin)
>> - Disable RSS write only in generic mode eventdev_pipeline. (Jerin)
>> - Modify set_supported_ptypes function to return successfuly set mask
>>    instead of failure.
>> - Dropped set_supported_ptypes to drivers by handling in library
>>    layer, interested PMD can add it in.
>>
>> Pavan Nikhilesh (7):
>>    ethdev: add set ptype function
>>    ethdev: add mbuf RSS update as an offload
>>    ethdev: add flow action type update as an offload
>>    drivers/net: update Rx RSS hash offload capabilities
>>    drivers/net: update Rx flow flag and mark capabilities
>>    examples/eventdev_pipeline: add new Rx RSS hash offload
>>    examples: disable Rx packet type parsing
> <...>