Re: [PATCH v2] net/iavf: revert fix VLAN insertion

[Kevin Traynor <ktraynor@redhat.com>]

On 20/10/2022 02:33, Zhou, YidingX wrote:
> 
> 
>> -----Original Message-----
>> From: Kevin Traynor <ktraynor@redhat.com>
>> Sent: Wednesday, October 19, 2022 4:53 PM
>> To: Zhou, YidingX <yidingx.zhou@intel.com>; dev@dpdk.org
>> Subject: Re: [PATCH v2] net/iavf: revert fix VLAN insertion
>>
>> On 19/10/2022 08:54, Yiding Zhou wrote:
>>> When the kernel driver tells to use the L2TAG2 field for VLAN
>>> insertion, the context descriptor needs to be used. There is an issue
>>> on the vector Tx path, because it does not support the context descriptor.
>>>
>>> The previous commit forces to select normal path to avoid the above
>>> issue, but it results in a performance loss of around 40%. So it needs
>>> to be reverted and the original issue needed to be fixed by rework.
>>>
>>
>> Thank you, that is a much clearer explanation.
>>
>> Now on the approach, the commit being reverted says:
>> "When the driver tells the VF to insert VLAN tag using the L2TAG2 field, vector
>> Tx path does not use Tx context descriptor and would cause VLAN tag inserted
>> into the wrong location."
>>
>> So it means this revert is solving a performance regression, but re-introducing
>> the functional issue above.
>>
>> Is there a correct fix for the original issue sent that can be applied too? If not,
>> wouldn't it be better to wait until it is before doing the revert?
>>
> 
> Sorry, there is no correct fix yet.
> We plan to support context descriptor on vector path to fix the original issue,
> It may take more time and cannot be completed within this cycle.
> 

ok, but you didn't answer the second question.

"When the driver tells the VF to insert VLAN tag using the L2TAG2 field, 
vector Tx path does not use Tx context descriptor and would cause VLAN 
tag inserted into the wrong location."

Please explain your justification for (re-)introducing this bug?

Why is better to get (corrupt?) packets with incorrect VLAN tags than 
lose performance for this case? Or have I mis-interpreted the patches.


>>> To reverts
>>> commit 0d58caa7d6d1 ("net/iavf: fix VLAN insertion")
>>>
>>> Fixes: 0d58caa7d6d1 ("net/iavf: fix VLAN insertion")
>>>
>>> Signed-off-by: Yiding Zhou <yidingx.zhou@intel.com>
>>> ---
>>>    drivers/net/iavf/iavf_rxtx_vec_common.h | 3 ---
>>>    1 file changed, 3 deletions(-)
>>>
>>> diff --git a/drivers/net/iavf/iavf_rxtx_vec_common.h
>>> b/drivers/net/iavf/iavf_rxtx_vec_common.h
>>> index 4ab22c6b2b..a59cb2ceee 100644
>>> --- a/drivers/net/iavf/iavf_rxtx_vec_common.h
>>> +++ b/drivers/net/iavf/iavf_rxtx_vec_common.h
>>> @@ -253,9 +253,6 @@ iavf_tx_vec_queue_default(struct iavf_tx_queue *txq)
>>>    	if (txq->offloads & IAVF_TX_NO_VECTOR_FLAGS)
>>>    		return -1;
>>>
>>> -	if (txq->vlan_flag == IAVF_TX_FLAGS_VLAN_TAG_LOC_L2TAG2)
>>> -		return -1;
>>> -
>>>    	if (txq->offloads & IAVF_TX_VECTOR_OFFLOAD)
>>>    		return IAVF_VECTOR_OFFLOAD_PATH;
>>>
>