> > > > > > > > > > > > > > > > > > > > > > > > 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. 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). If we'll find there is no real difference - move it to not-inlined version in 19.08. It is experimental for now - so could be changed without formal ABI breakage. Konstantin
