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

[Matan Azrad <matan@mellanox.com>]

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.


> > 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.