Re: [dpdk-dev] [dpdk-stable] [PATCH 1/2] app/testpmd: fix scatter offload configuration

["Yigit, Ferruh" <ferruh.yigit@linux.intel.com>]

On 7/31/2019 7:11 AM, Matan Azrad wrote:
> Hi Ferruh
> 
> From: Ferruh Yigit
>> On 7/30/2019 7:34 PM, Matan Azrad wrote:
>>>
>>>
>>> From: Ferruh Yigit
>>>> On 7/30/2019 4:56 PM, Matan Azrad wrote:
>>>>> Hi Ferruh
>>>>>
>>>>>  From: Ferruh Yigit
>>>>>> Sent: Tuesday, July 30, 2019 6:22 PM
>>>>>> To: Matan Azrad <matan@mellanox.com>; Wenzhuo Lu
>>>>>> <wenzhuo.lu@intel.com>; Jingjing Wu <jingjing.wu@intel.com>
>>>>>> Cc: dev@dpdk.org; stable@dpdk.org
>>>>>> Subject: Re: [dpdk-dev] [PATCH 1/2] app/testpmd: fix scatter
>>>>>> offload configuration
>>>>>>
>>>>>> On 7/30/2019 2:17 PM, Matan Azrad wrote:
>>>>>>> Hi Ferruh
>>>>>>>
>>>>>>> From: Ferruh Yigit
>>>>>>>> Sent: Tuesday, July 30, 2019 4:09 PM
>>>>>>>> To: Matan Azrad <matan@mellanox.com>; Wenzhuo Lu
>>>>>>>> <wenzhuo.lu@intel.com>; Jingjing Wu <jingjing.wu@intel.com>
>>>>>>>> Cc: dev@dpdk.org; stable@dpdk.org
>>>>>>>> Subject: Re: [dpdk-dev] [PATCH 1/2] app/testpmd: fix scatter
>>>>>>>> offload configuration
>>>>>>>>
>>>>>>>> On 7/29/2019 1:36 PM, Matan Azrad wrote:
>>>>>>>>> When the mbuf data size cannot contain the maximum Rx packet
>>>>>>>>> length with the mbuf headroom, a packet should be scattered in
>>>>>>>>> more than one
>>>>>>>> mbuf.
>>>>>>>>>
>>>>>>>>> The application did not configure scatter offload in the above case.
>>>>>>>>>
>>>>>>>>> Enable the Rx scatter offload in the above case.
>>>>>>>>>
>>>>>>>>> Fixes: 33f9630fc23d ("app/testpmd: create mbuf based on max
>>>>>>>>> supported
>>>>>>>>> segments")
>>>>>>>>> Cc: stable@dpdk.org
>>>>>>>>>
>>>>>>>>> Signed-off-by: Matan Azrad <matan@mellanox.com>
>>>>>>>>
>>>>>>>> Deferring the patchset to next release, they were late anyway and
>>>>>>>> not actually fixing a defect, safer to defer than getting them in rc3.
>>>>>>>
>>>>>>> Yes this patch came late for RC3 but it is a fix.
>>>>>>>
>>>>>>> What are you concerns here?
>>>>>>> Why don't you think defect found?
>>>>>>
>>>>>> First patch changes the behavior, when mbuf size is larger than
>>>>>> configured size and user didn't provided the scatter offload,
>>>>>> should test application automatically enable it?
>>>>>
>>>>> No, only when the mbuf size is smaller than the max_rx_pkt_len with
>>>> headroom.
>>>>> If scatter is not enabled in the above case, how can the PMD provide
>>>>> a
>>>> packet with max_rx_pkt_len size?
>>>>>
>>>
>>> Answer here?
>>
>> Is it because drivers also "automatically" enable scattered Rx based on other
>> values?
> 
> Scatter is a defined RX offload.
> Like other offloads I think it always should be explicitly set by the user if he wants it, and vice versa.
> If the user doesn't configure it, the PMD should not scatter packets because the user doesn't expect multi-mbuf packets in datapath and maybe even doesn't handle it.

+1

So what about having the log message but not implicitly update the offload config?

> 
> So, I think the above case is a user conflict in Rx configuration and like other conflicts it should cause an error.
> In MLX5 PMD, an error will be returned from Rx setup.
> 
>