[dpdk-dev] ABI and inline functions

[Ray Kinsella]

On 17/04/2019 19:51, Stephen Hemminger wrote:
> On Wed, 17 Apr 2019 17:46:34 +0000
> Jerin Jacob Kollanukkaran <jerinj at marvell.com> wrote:
> 
>>> -----Original Message-----
>>> From: dev <dev-bounces at dpdk.org> On Behalf Of Bruce Richardson
>>> Sent: Wednesday, April 17, 2019 2:07 PM
>>> To: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>
>>> Cc: dev at dpdk.org; Stephen Hemminger <stephen at networkplumber.org>;
>>> Ananyev, Konstantin <konstantin.ananyev at intel.com>; thomas at monjalon.net;
>>> Ray Kinsella <mdr at ashroe.eu>; nd <nd at arm.com>
>>> Subject: Re: [dpdk-dev] ABI and inline functions
>>>   
>>>> 2) Every function that is not in the direct datapath (fastpath?)
>>>> should not be inline. Exceptions or things like rx/tx burst, ring
>>>> enqueue/dequeue, and packet alloc/free - Stephen  
>>>
>>> Agree with this. Anything not data path should not be inline. The next question
>>> then is for data path items how to determine whether they need to be inline or
>>> not. In general my rule-of-thumb:
>>> * anything dealing with bursts of packets should not be inline  
>>
>> # I think, we need consider the how fat is the function too,
>> If it is light weight, probably we need to make it inline

Well if it light weight however it is not dealing directly with packets,
probably does not matter if is not-inline?

>> # Except the forward case, In real world use case, it is not trivial make large 
>> burst of packet to process it even though function prototype burst.
>> We may need to consider that

>> # For the given function if some argument is used with inline other function,
>>  probably no point in making that function alone  inline as the structure 
>> is exposed in some other function.
>>
>>> * anything what works with single packet at a time should be inline
>>>   
>>>> In this context, does it make sense to say that we will maintain API
>>>> compatibility rather than saying ABI compatibility? This will also
>>>> send the right message to the end users.
>>>>  
>>> I would value ABI compatibility much higher than API compatibility. If someone
>>> is recompiling the application anyway, making a couple of small changes (large
>>> rework is obviously a different issue) to the code should not be a massive issue, I
>>> hope. On the other hand, ABI compatibility is needed to allow seamless update
>>> from one version to another, and it's that ABI compatiblity that allows distro's to
>>> pick up our latest and greatest versions.  
>>
>> IMO, We have two primary use case for DPDK
>>
>> 1) NFV kind of use case 	where the application needs to run on multiple platform
>> without recompiling it.
>> 2) Fixed appliance use case where embed SoC like Intel Denverton or ARM64 integrated
>> Controller used. For fixed appliance use case, end user care more of performance
>> than ABI compatibility as it easy to recompile the end user application vs the cost of
>> hitting performance impact.
> 
> Nobody cares about compatiablity until they have to the first security update.
>  
+1