On 28/10/2020 15:22, Honnappa Nagarahalli wrote:
> + Ray for ABI
>
> <snip>
>
>>
>> On Wed, Oct 28, 2020 at 02:28:43PM +0000, Akhil Goyal wrote:
>>>
>>> Hi Konstantin,
>>>
>>>>>> Hi Tech board members,
>>>>>>
>>>>>> I have a doubt about the ABI breakage in below addition of field.
>>>>>> Could you please comment.
>>>>>>
>>>>>>> /** The data structure associated with each crypto device. */
>>>>>>> struct rte_cryptodev {
>>>>>>> dequeue_pkt_burst_t dequeue_burst; @@ -867,6 +922,10
>> @@
>>>>>>> struct rte_cryptodev {
>>>>>>> __extension__
>>>>>>> uint8_t attached : 1;
>>>>>>> /**< Flag indicating the device is attached */
>>>>>>> +
>>>>>>> + struct rte_cryptodev_enq_cb_rcu *enq_cbs;
>>>>>>> + /**< User application callback for pre enqueue processing */
>>>>>>> +
>>>>>>> } __rte_cache_aligned;
>>>>>>
>>>>>> Here rte_cryptodevs is defined in stable API list in map file
>>>>>> which is a pointer To all rte_cryptodev and the above change is
>>>>>> changing the size of the
>>>> structure.
>>>>
>>>> While this patch adds new fields into rte_cryptodev structure, it
>>>> doesn't change the size of it.
>>>> struct rte_cryptodev is cache line aligned, so it's current size:
>>>> 128B for 64-bit systems, and 64B(/128B) for 32-bit systems.
>>>> So for 64-bit we have 47B implicitly reserved, and for 32-bit we
>>>> have 19B reserved.
>>>> That's enough to add two pointers without changing size of this struct.
>>>>
>>>
>>> The structure is cache aligned, and if the cache line size in 32Byte
>>> and the compilation is done on 64bit machine, then we will be left
>>> with 15Bytes which is not sufficient for 2 pointers.
>>> Do we have such systems? Am I missing something?
>>>
>>
>> I don't think we support any such systems, so unless someone can point out
>> a specific case where we need to support 32-byte CLs, I'd tend towards
>> ignoring this as a non-issue.
> Agree. I have not come across 32B cache line.
>
>>
>>> The reason I brought this into techboard is to have a consensus on
>>> such change As rte_cryptodev is a very popular and stable structure.
>>> Any changes to it may Have impacts which one person cannot judge all use
>> cases.
>>>
>>
>> Haven't been tracking this discussion much, but from what I read here, this
>> doesn't look like an ABI break and should be ok.
> If we are filling the holes in the cache line with new fields, it should not
> be an ABI break.
Agreed, risk seems minimal ... it is an ABI Breakage window in anycase.
>>
>> Regards,
>> /Bruce
