<snip> > > >>>>>>>>> Current mempool per core cache implementation is based on > > >>>>> pointer > > >>>>>>>>> For most architectures, each pointer consumes 64b Replace it > > >>>>> with > > >>>>>>>>> index-based implementation, where in each buffer is > > >>>>>>>>> addressed > > >>>>> by > > >>>>>>>>> (pool address + index) > > >>>> > > >>>> I like Dharmik's suggestion very much. CPU cache is a critical > > >>>> and limited resource. > > >>>> > > >>>> DPDK has a tendency of using pointers where indexes could be used > > >>>> instead. I suppose pointers provide the additional flexibility of > > >>>> mixing entries from different memory pools, e.g. multiple mbuf > > >> pools. > > >>>> > > >> > > >> Agreed, thank you! > > >> > > >>>>>>>> > > >>>>>>>> I don't think it is going to work: > > >>>>>>>> On 64-bit systems difference between pool address and it's > > elem > > >>>>>>>> address could be bigger than 4GB. > > >>>>>>> Are you talking about a case where the memory pool size is > > >>>>>>> more > > >>>>> than 4GB? > > >>>>>> > > >>>>>> That is one possible scenario. > > >>>> > > >>>> That could be solved by making the index an element index instead > > of > > >> a > > >>>> pointer offset: address = (pool address + index * element size). > > >>> > > >>> Or instead of scaling the index with the element size, which is > > only > > >> known at runtime, the index could be more efficiently scaled by a > > >> compile time constant such as RTE_MEMPOOL_ALIGN (= > > >> RTE_CACHE_LINE_SIZE). With a cache line size of 64 byte, that would > > >> allow indexing into mempools up to 256 GB in size. > > >>> > > >> > > >> Looking at this snippet [1] from rte_mempool_op_populate_helper(), > > >> there is an ‘offset’ added to avoid objects to cross page > > boundaries. > > >> If my understanding is correct, using the index of element instead > > of a > > >> pointer offset will pose a challenge for some of the corner cases. > > >> > > >> [1] > > >> for (i = 0; i < max_objs; i++) { > > >> /* avoid objects to cross page boundaries */ > > >> if (check_obj_bounds(va + off, pg_sz, total_elt_sz) > > >> < > > >> 0) { > > >> off += RTE_PTR_ALIGN_CEIL(va + off, pg_sz) - > > >> (va + off); > > >> if (flags & RTE_MEMPOOL_POPULATE_F_ALIGN_OBJ) > > >> off += total_elt_sz - > > >> (((uintptr_t)(va + off - 1) % > > >> total_elt_sz) + 1); > > >> } > > >> > > > > > > OK. Alternatively to scaling the index with a cache line size, you > > can scale it with sizeof(uintptr_t) to be able to address 32 or 16 GB > > mempools on respectively 64 bit and 32 bit architectures. Both x86 and > > ARM CPUs have instructions to access memory with an added offset > > multiplied by 4 or 8. So that should be high performance. > > > > Yes, agreed this can be done. > > Cache line size can also be used when ‘MEMPOOL_F_NO_CACHE_ALIGN’ is > > not enabled. > > On a side note, I wanted to better understand the need for having the > > 'MEMPOOL_F_NO_CACHE_ALIGN' option. > > The description of this field is misleading, and should be corrected. > The correct description would be: Don't need to align objs on cache lines. > > It is useful for mempools containing very small objects, to conserve memory. I think we can assume that mbuf pools are created with the 'MEMPOOL_F_NO_CACHE_ALIGN' flag set. With this we can use offset calculated with cache line size as the unit.
> > > > > > > > >>>> > > >>>>>> Another possibility - user populates mempool himself with some > > >>>>> external > > >>>>>> memory by calling rte_mempool_populate_iova() directly. > > >>>>> Is the concern that IOVA might not be contiguous for all the > > memory > > >>>>> used by the mempool? > > >>>>> > > >>>>>> I suppose such situation can even occur even with normal > > >>>>>> rte_mempool_create(), though it should be a really rare one. > > >>>>> All in all, this feature needs to be configurable during compile > > >>>> time. > > >>> > > >