> On Nov 3, 2021, at 10:52 AM, Morten Brørup <m...@smartsharesystems.com> wrote: > >> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Dharmik Thakkar >> Sent: Wednesday, 3 November 2021 16.13 >> >> Hi, >> >> Thank you everyone for the comments! I am currently working on making >> the global pool ring’s implementation as index based. >> Once done, I will send a patch for community review. I will also make >> it as a compile time option. > > Sounds good to me. > > This could probably be abstracted to other libraries too. E.g. the ring > library holds pointers to objects (void *); an alternative ring library could > hold indexes to objects (uint32_t). A ring often holds objects from the same > mempool, and the application knows which mempool, so indexing would be useful > here too. >
Yes, ring library within DPDK has the APIs to support configurable element size >> >>> On Oct 31, 2021, at 3:14 AM, Morten Brørup <m...@smartsharesystems.com> >> wrote: >>> >>>> From: Morten Brørup >>>> Sent: Saturday, 30 October 2021 12.24 >>>> >>>>> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Honnappa >>>>> Nagarahalli >>>>> Sent: Monday, 4 October 2021 18.36 >>>>> >>>>> <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. > >>>> >>>>>> 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. >>> >
