> > > > > > > > > > > > > > > > > > > > > > > > > > After evaluating long term API/ABI issues, I > > > > > > > > > > > > > think you need to get rid of almost all use of > > > > > > > > > > > > > inline and visible structures. Yes it might be > > > > > > > > > > > > > marginally slower, but you thank me > > > > > > > the first time you have to fix something. > > > > > > > > > > > > > > > > > > > > > > > > > Agree, I was planning on another version to > > > > > > > > > > > > address this (I am yet > > > > > > > to take a look at your patch addressing the ABI). > > > > > > > > > > > > The structure visibility definitely needs to be > addressed. > > > > > > > > > > > > For the inline functions, is the plan to convert > > > > > > > > > > > > all the inline functions in DPDK? If yes, I think > > > > > > > > > > > > we need to consider the performance > > > > > > > > > > > difference. May be consider L3-fwd application, > > > > > > > > > > > change all the > > > > > > > inline functions in its path and run a test? > > > > > > > > > > > > > > > > > > > > > > Every function that is not in the direct datapath > > > > > > > > > > > should not be > > > > > > > inline. > > > > > > > > > > > Exceptions or things like rx/tx burst, ring > > > > > > > > > > > enqueue/dequeue, and packet alloc/free > > > > > > I do not understand how DPDK can claim ABI compatibility if we > > > > > > have > > > > > inline functions (unless we freeze any development in these > > > > > inline functions forever). > > > > > > > > > > > > > > > > > > > > > > > > > > Plus synchronization routines: spin/rwlock/barrier, etc. > > > > > > > > > > I think rcu should be one of such exceptions - it is > > > > > > > > > > just another synchronization mechanism after all (just > > > > > > > > > > a bit more > > > > > sophisticated). > > > > > > > > > > Konstantin > > > > > > > > > > > > > > > > > > If you look at the other userspace RCU, you wil see that > > > > > > > > > the only inlines are the rcu_read_lock,rcu_read_unlock > > > > > > > > > and > > > > > > > rcu_reference/rcu_assign_pointer. > > > > > > > > > > > > > > > > > > The synchronization logic is all real functions. > > > > > > > > > > > > > > > > In fact, I think urcu provides both flavors: > > > > > > > > https://github.com/urcu/userspace- > > > > > > > rcu/blob/master/include/urcu/static/ > > > > > > > > urcu-qsbr.h I still don't understand why we have to treat > > > > > > > > it differently then let say spin-lock/ticket-lock or rwlock. > > > > > > > > If we gone all the way to create our own version of rcu, > > > > > > > > we probably want it to be as fast as possible (I know that > > > > > > > > main speedup should come from the fact that readers don't > > > > > > > > have to wait for writer to finish, but still...) > > > > > > > > > > > > > > > > Konstantin > > > > > > > > > > > > > > > > > > > > > > Having locking functions inline is already a problem in > > > > > > > current > > > releases. > > > > > > > The implementation can not be improved without breaking ABI > > > > > > > (or doing special workarounds like lock v2) > > > > > > I think ABI and inline function discussion needs to be taken > > > > > > up in a > > > > > different thread. > > > > > > > > > > > > Currently, I am looking to hide the structure visibility. I > > > > > > looked at your > > > > > patch [1], it is a different case than what I have in this > > > > > patch. It is a pretty generic use case as well (similar > > > > > situation exists in other libraries). I think a generic solution > > > > > should > be agreed upon. > > > > > > > > > > > > If we have to hide the structure content, the handle to QS > > > > > > variable > > > > > returned to the application needs to be opaque. I suggest using > 'void *' > > > > > behind which any structure can be used. > > > > > > > > > > > > typedef void * rte_rcu_qsbr_t; typedef void * rte_hash_t; > > > > > > > > > > > > But it requires typecasting. > > > > > > > > > > > > [1] http://patchwork.dpdk.org/cover/52609/ > > > > > > > > > > C allows structure to be defined without knowing what is in it > > > therefore. > > > > > > > > > > typedef struct rte_rcu_qsbr rte_rcu_qsbr_t; > > > > > > > > > > is preferred (or do it without typedef) > > > > > > > > > > struct rte_rcu_qsbr; > > > > > > > > I see that rte_hash library uses the same approach (struct > > > > rte_hash in > > > rte_hash.h, though it is marking as internal). But the ABI > > > Laboratory tool [1] seems to be reporting incorrect numbers for this > > > library even though the internal structure is changed. > > > > > > > > [1] > > > > https://abi- > > > laboratory.pro/index.php?view=compat_report&l=dpdk&v1=19.0 > > > > 2&v2=current&obj=66794&kind=abi > > > > > > The problem is rte_hash structure is exposed as part of ABI in > > > rte_cuckoo_hash.h This was a mistake. > > Do you mean, due to the use of structure with the same name? I am > > wondering if it is just a tools issue. The application is not supposed to > include rte_cuckoo_hash.h. > > > > For the RCU library, we either need to go all functions or leave it > > the way it is. I do not see a point in trying to hide the internal structure > while having inline functions. > > > > I converted the inline functions to function calls. > > > > Testing on Arm platform (results *are* repeatable) shows very minimal > > drop (0.1% to 0.2%) in performance while using lock-free rte_hash data > structure. But one of the test cases which is just spinning shows good > amount of drop (41%). > > > > Testing on x86 (Xeon Gold 6132 CPU @ 2.60GHz, results *are* pretty > > repeatable) shows performance improvements (7% to 8%) while using > lock-free rte_hash data structure. The test cases which is just spinning > show significant drop (14%, 155%, 231%). > > Konstantin, any thoughts on the results? > > The fact that function show better result than inline (even for hash) is sort > of surprise to me. It was a surprise to me too and counter-intuitive to my understanding. > Don't have any good explanation off-hand, but the actual numbers for > hash test are huge by itself... > > In general, I still think that sync primitives better to stay inlined - there > is > no much point to create ones and then figure out that no-one using them > because they are too slow. > Though if there is no real perf difference between inlined and normal - no > point to keep it inlined. > About RCU lib, my thought to have inlined version for 19.05 and do > further perf testing with it (as I remember there were suggestions about > using it in l3fwd for guarding routing table or so). Yes, there is more work planned to integrate the library better which might provide more insight.
> If we'll find there is no real difference - move it to not-inlined version in > 19.08. +1. > It is experimental for now - so could be changed without formal ABI > breakage. > > Konstantin > >
