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

[Thomas Monjalon <thomas@monjalon.net>]

16/01/2018 18:38, Burakov, Anatoly:
> 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 :)

To be on the safe side, you announce a deprecation.
And there will be no debate in 18.05 (except if someone has a better idea).