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

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

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? 
> 
> I think not enabling scatter in this case it is a user conflict in configuration and should raise an error in the PMD.  Maybe even in ethdev layer.
> 
>> It may or not, but this is the change of the behavior, I
>> think not a fix.
>>
>> And second patch adds more detail into the statistics, so I believe it is clear
>> that it is not a fix.
>  
>  Agree, this can wait.
> 
>> The concern is getting changes very close to release, to balance between risk
>> and benefit of the feature. I don't see any reason why these changes can't
>> wait next release, so I don't see any reason to get the risk.
> 
> When  I changed the default max_rx_pkt_len and mbuf size in LRO testing I met this issue.
> 
> By default scatter will not be enabled.

I think it is still arguable if scatter should be enabled by default, but isn't
there a way in testpmd to enable scatter explicitly? If so you have a way to
test LRO.

> 
> 
>>> What's about RC4?
>>
>> No, it is even worse, there will be only a little testing after rc4 and a little time
>> before release.
> 
> So, I hope it will be integrated in RC3.
>