Re: [dpdk-dev] [PATCH v15 3/7] ethdev: add validation to offloads set by PMD

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 11/3/19 6:16 PM, Matan Azrad wrote
> From: Andrew Rybchenko
>> On 11/3/19 9:57 AM, Matan Azrad wrote:
>>> Hi
>>>
>>> From: Andrew Rybchenko
>>>> On 10/31/19 7:33 PM, Pavan Nikhilesh Bhagavatula wrote:
>>>>>> From: Pavan Nikhilesh Bhagavatula
>>>>>>> Hi Matan,
>>>>>>>
>>>>>>>> Hi Pavan
>>>>>>>>
>>>>>>>> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>>>>>>>> Some PMDs cannot work when certain offloads are
>> enable/disabled,
>>>>>>>>> as a workaround PMDs auto enable/disable offloads internally and
>>>>>>>>> expose it through dev->data->dev_conf.rxmode.offloads.
>>>>>>>>>
>>>>>>>>> After device specific dev_configure is called compare the
>>>>>>>>> requested offloads to the offloads exposed by the PMD and, if
>>>>>>>>> the PMD failed to enable a given offload then log it and return
>>>>>>>>> -EINVAL from rte_eth_dev_configure, else if the PMD failed to
>>>>>>>>> disable a given offload log and continue with
>> rte_eth_dev_configure.
>>>>>>>>>
>>>>>>>> rte_eth_dev_configure can be called more than 1 time in the
>>>>>>>> device life time, How can you know what is the minimum offload
>>>>>>>> configurations required by the port after the first call?
>>>>>>>> Maybe putting it in dev info is better, what do you think?
>>>>>>>>
>>>>>>> We only return -EINVAL in the case where we enable an offload
>>>>>>> advertised by dev_info and the port still fails to enable it.
>>>>>> Are you sure it is ok that devices may disable\enable offloads
>>>>>> under the hood without user notification?
>>>>> Some devices already do it. The above check adds validation for the same.
>>>> The problem is that some offloads cannot be disabled.
>>> Yes, I understand it.
>>>
>>>> If application does not request Rx checksum offload since it does use
>>>> it, it is not a problem to report it.
>>> Yes, for RX checksum I tend to agree that application doesn't care if the
>> PMD will calculate the checksum in spite of the offload is disabled.
>>>
>>> But what's about other offloads:
>>> For example in RX: LRO, CRC_KEEP, VLAN_STRIP, JUMBO If the PMD will
>>> stay them on while the app is disabling it, It can cause a problems to the
>> application (affects the packet length).
>>
>> Yes, I agree that some offloads are critical to be disabled, but RSS_HASH
>> discussed in the changeset is not critical.
> 
> So, are you agree It should not be checked globally for all the offloads in ethdev layer?

If offload is not requested, but enabled (since PMD cannot disable it),
right not it will not fail configure, but warn about it in logs.

> It even be more problematic if the dynamic offload field in mbuf is not exist at all.  
> 
>>
>>> For example in TX: TSO, VLAN, MULTI_SEG.....
>>
>> Tx is not that critical since application should not request these offloads per-
>> packet. Tx offloads are mainly required to ensure that application may
>> request the offload per packet and it will be done.
> 
> yes, you right, In TX it looks less critical (for now).
> 
>>
>>>> Of course, it could be a problem if the offload is used, but
>>>> application wants to disable it, for example, for debugging purposes.
>>>> In this case, the solution is to mask offloads on application level,
>>>> which is not ideal as well.
>>> Why not ideal?
>>
>> It eats CPU cycles.
> 
> Sorry, I don't understand your use case here.

If application wants to try code path without, for example,
Rx checksum offload, it could be insufficient to disable
the offload right now, but also required to cleanup offload
results flags in each mbuf (if PMD does not support the
offload disabling).

>>> If application can know the limitation of offloads disabling (for example to
>> read capability on it)
>>> The application has all information to take decisions.
>>>
>>>> Anyway, the patch just tries to highlight difference of applied from
>>>> requested. So, it is a step forward.
>>>> Also, the patch will fail configure if an offload is requested, but not
>> enabled.
>>>>
>>>>>> Can't it break applications?
>>>>>> Why does the device expose unsupported offloads in dev info?
>>>>>> Does it update the running offload usynchronically? Race?
>>>>>> Can you explain also your specific use case?
>>>>>>
>>>>>>
>>>>>>>> Matan
>