Re: [dpdk-dev] [PATCH 01/27] eventdev: dlb upstream prerequisites

["Kinsella, Ray" <mdr@ashroe.eu>]

On 30/06/2020 13:14, Jerin Jacob wrote:
> On Tue, Jun 30, 2020 at 5:06 PM Kinsella, Ray <mdr@ashroe.eu> wrote:
>>
>>
>>
>> On 30/06/2020 12:30, Jerin Jacob wrote:
>>> On Tue, Jun 30, 2020 at 4:52 PM Kinsella, Ray <mdr@ashroe.eu> wrote:
>>>>
>>>>
>>>>
>>>> On 27/06/2020 08:44, Jerin Jacob wrote:
>>>>>> +
>>>>>> +/** Event port configuration structure */
>>>>>> +struct rte_event_port_conf_v20 {
>>>>>> +       int32_t new_event_threshold;
>>>>>> +       /**< A backpressure threshold for new event enqueues on this port.
>>>>>> +        * Use for *closed system* event dev where event capacity is limited,
>>>>>> +        * and cannot exceed the capacity of the event dev.
>>>>>> +        * Configuring ports with different thresholds can make higher priority
>>>>>> +        * traffic less likely to  be backpressured.
>>>>>> +        * For example, a port used to inject NIC Rx packets into the event dev
>>>>>> +        * can have a lower threshold so as not to overwhelm the device,
>>>>>> +        * while ports used for worker pools can have a higher threshold.
>>>>>> +        * This value cannot exceed the *nb_events_limit*
>>>>>> +        * which was previously supplied to rte_event_dev_configure().
>>>>>> +        * This should be set to '-1' for *open system*.
>>>>>> +        */
>>>>>> +       uint16_t dequeue_depth;
>>>>>> +       /**< Configure number of bulk dequeues for this event port.
>>>>>> +        * This value cannot exceed the *nb_event_port_dequeue_depth*
>>>>>> +        * which previously supplied to rte_event_dev_configure().
>>>>>> +        * Ignored when device is not RTE_EVENT_DEV_CAP_BURST_MODE capable.
>>>>>> +        */
>>>>>> +       uint16_t enqueue_depth;
>>>>>> +       /**< Configure number of bulk enqueues for this event port.
>>>>>> +        * This value cannot exceed the *nb_event_port_enqueue_depth*
>>>>>> +        * which previously supplied to rte_event_dev_configure().
>>>>>> +        * Ignored when device is not RTE_EVENT_DEV_CAP_BURST_MODE capable.
>>>>>> +        */
>>>>>>         uint8_t disable_implicit_release;
>>>>>>         /**< Configure the port not to release outstanding events in
>>>>>>          * rte_event_dev_dequeue_burst(). If true, all events received through
>>>>>> @@ -733,6 +911,14 @@ struct rte_event_port_conf {
>>>>>>  rte_event_port_default_conf_get(uint8_t dev_id, uint8_t port_id,
>>>>>>                                 struct rte_event_port_conf *port_conf);
>>>>>>
>>>>>> +int
>>>>>> +rte_event_port_default_conf_get_v20(uint8_t dev_id, uint8_t port_id,
>>>>>> +                               struct rte_event_port_conf_v20 *port_conf);
>>>>>> +
>>>>>> +int
>>>>>> +rte_event_port_default_conf_get_v21(uint8_t dev_id, uint8_t port_id,
>>>>>> +                                     struct rte_event_port_conf *port_conf);
>>>>>
>>>>> Hi Timothy,
>>>>>
>>>>> + ABI Maintainers (Ray, Neil)
>>>>>
>>>>> # As per my understanding, the structures can not be versioned, only
>>>>> function can be versioned.
>>>>> i.e we can not make any change to " struct rte_event_port_conf"
>>>>
>>>> So the answer is (as always): depends
>>>>
>>>> If the structure is being use in inline functions is when you run into trouble
>>>> - as knowledge of the structure is embedded in the linked application.
>>>>
>>>> However if the structure is _strictly_ being used as a non-inlined function parameter,
>>>> It can be safe to version in this way.
>>>
>>> But based on the optimization applied when building the consumer code
>>> matters. Right?
>>> i.e compiler can "inline" it, based on the optimization even the
>>> source code explicitly mentions it.
>>
>> Well a compiler will typically only inline within the confines of a given object file, or
>> binary, if LTO is enabled.
> 
>>
>> If a function symbol is exported from library however, it won't be inlined in a linked application.
> 
> Yes, With respect to that function.
> But the application can use struct rte_event_port_conf in their code
> and it can be part of other structures.
> Right?

Tim, it looks like you might be inadvertently breaking other symbols also.
For example ... 

int
rte_event_crypto_adapter_create(uint8_t id, uint8_t dev_id,
                                struct rte_event_port_conf *port_config,
                                enum rte_event_crypto_adapter_mode mode);

int
rte_event_port_setup(uint8_t dev_id, uint8_t port_id,
                     const struct rte_event_port_conf *port_conf);

These and others symbols are also using rte_event_port_conf and would need to be updated to use the v20 struct,
if we aren't to break them . 

> 
> 
>> The compiler doesn't have enough information to inline it.
>> All the compiler will know about it is it's offset in memory, and it's signature.
>>
>>>
>>>
>>>>
>>>> So just to be clear, it is still the function that is actually being versioned here.
>>>>
>>>>>
>>>>> # We have a similar case with ethdev and it deferred to next release v20.11
>>>>> http://patches.dpdk.org/patch/69113/
>>>>
>>>> Yes - I spent a why looking at this one, but I am struggling to recall,
>>>> why when I looked it we didn't suggest function versioning as a potential solution in this case.
>>>>
>>>> Looking back at it now, looks like it would have been ok.
>>>
>>> Ok.
>>>
>>>>
>>>>>
>>>>> Regarding the API changes:
>>>>> # The slow path changes general looks good to me. I will review the
>>>>> next level in the coming days
>>>>> # The following fast path changes bothers to me. Could you share more
>>>>> details on below change?
>>>>>
>>>>> diff --git a/app/test-eventdev/test_order_atq.c
>>>>> b/app/test-eventdev/test_order_atq.c
>>>>> index 3366cfc..8246b96 100644
>>>>> --- a/app/test-eventdev/test_order_atq.c
>>>>> +++ b/app/test-eventdev/test_order_atq.c
>>>>> @@ -34,6 +34,8 @@
>>>>>                         continue;
>>>>>                 }
>>>>>
>>>>> +               ev.flow_id = ev.mbuf->udata64;
>>>>> +
>>>>> # Since RC1 is near, I am not sure how to accommodate the API changes
>>>>> now and sort out ABI stuffs.
>>>>> # Other concern is eventdev spec get bloated with versioning files
>>>>> just for ONE release as 20.11 will be OK to change the ABI.
>>>>> # While we discuss the API change, Please send deprecation notice for
>>>>> ABI change for 20.11,
>>>>> so that there is no ambiguity of this patch for the 20.11 release.
>>>>>