Re: [dpdk-dev] [PATCH v2] eal: add function to return number of detected sockets

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 16-Jan-18 5:34 PM, Thomas Monjalon wrote:
> 16/01/2018 16:05, Burakov, Anatoly:
>> On 16-Jan-18 12:20 PM, Thomas Monjalon wrote:
>>> 16/01/2018 12:56, Burakov, Anatoly:
>>>> On 12-Jan-18 11:50 AM, Thomas Monjalon wrote:
>>>>> 12/01/2018 12:44, Burakov, Anatoly:
>>>>>> On 11-Jan-18 10:20 PM, Thomas Monjalon wrote:
>>>>>>> 22/12/2017 13:41, Anatoly Burakov:
>>>>>>>> During lcore scan, find maximum socket ID and store it.
>>>>>>>>
>>>>>>>> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
>>>>>>>> ---
>>>>>>>> --- a/lib/librte_eal/common/include/rte_eal.h
>>>>>>>> +++ b/lib/librte_eal/common/include/rte_eal.h
>>>>>>>> @@ -83,6 +83,7 @@ enum rte_proc_type_t {
>>>>>>>>      struct rte_config {
>>>>>>>>      	uint32_t master_lcore;       /**< Id of the master lcore */
>>>>>>>>      	uint32_t lcore_count;        /**< Number of available logical cores. */
>>>>>>>> +	uint32_t numa_node_count;    /**< Number of detected NUMA nodes. */
>>>>>>>>      	uint32_t service_lcore_count;/**< Number of available service cores. */
>>>>>>>>      	enum rte_lcore_role_t lcore_role[RTE_MAX_LCORE]; /**< State of cores. */
>>>>>>>
>>>>>>> isn't it breaking the ABI?
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> Yep, you're right, forgot to add that. I didn't expect this to get
>>>>>> merged in 18.02 anyway, so v2 will follow.
>>>>>
>>>>> Please write 18.05 in the subject to show your expectation.
>>>>> Thanks
>>>>>
>>>>
>>>> Does it have to be an ABI change though? We can put numa_node_count
>>>> after pointer to mem_config, in which case it won't be an ABI break.
>>>> Would that be better?
>>>
>>> Changing the size of a struct which is allocated by the app,
>>> is an ABI break.
>>> Is your solution changing the size?
>>>
>>
>> It's not really allocated as such. rte_config is a global static
>> variable, and we only ever get pointers to it from the user code. If we
>> add the new value at the end, all of the old data layout would be intact
>> and work as before, so nothing would change as far as old code is concerned.
>>
>> However, if that's still considered an ABI break, then OK, break it is.
> 
> Maybe that assuming it is never allocated (not copied for instance)
> we could consider it is not an ABI break.
> 
>> Some background for why this is needed - for the memory hotplug, we need
>> to know how many sockets we can allocate memory at, to distinguish
>> between socket that doesn't exist, and socket that exists but has no
>> memory allocated on it. I'm OK with trying other approaches (such as
>> storing numa nodes in a static variable somewhere) if breaking ABI for
>> this is too much to ask for such a minute change.
> 
> Why is it important for 18.02?
> Memory hotplug will be integrated only in 18.05.
> I think it is better to just wait (and announce the deprecation).
> 

It isn't, i've already marked this patch as deferred. However, we'll 
have to have this discussion anyway :)

-- 
Thanks,
Anatoly