Hey Pragash, You can pass your own hash function to rte_hash_create() otherwise a default one will be used, see http://dpdk.org/browse/dpdk/tree/lib/librte_hash/rte_cuckoo_hash.c#n281
The default hash function is rte_hash_crc() or in some cases rte_jhash(), see http://dpdk.org/browse/dpdk/tree/lib/librte_hash/rte_cuckoo_hash.h#n61 You can find the implementation of rte_hash_crc() over here: http://dpdk.org/browse/dpdk/tree/lib/librte_hash/rte_hash_crc.h#n588 Please note there is a separate mailing list for DPDK usage discussions: http://dpdk.org/ml/listinfo/users The dev@ list is mostly for patch reviews and RFCs... Andriy On Thu, Aug 24, 2017 at 8:54 PM, Pragash Vijayaragavan <pxv3...@rit.edu> wrote: > Thats great, what about the hash functions. > > On 24 Aug 2017 10:54, "Andriy Berestovskyy" <a...@semihalf.com> wrote: >> >> Hey Pragash, >> I am not the author of the code, but I guess it is done that way >> because modern compilers do recognize power of two constants and do >> substitute division and modulo operations with corresponding bit >> manipulations. >> >> Just try to compile a small program like the following: >> >> volatile unsigned a = 123, b, c; >> int main(int argc, char **argv) >> { >> b = a / 4; >> c = a % 4; >> printf("%x %x %x\n", a, b, c); >> } >> >> >> and then disassemble it with gdb: >> >> (gdb) disassemble /s main >> [...] >> 13 b = a / 4; >> 0x0000000000400464 <+20>: shr $0x2,%eax >> 0x0000000000400467 <+23>: mov %eax,0x200bd3(%rip) # 0x601040 >> <b> >> >> 14 c = a % 4; >> 0x000000000040046d <+29>: mov 0x200bc5(%rip),%eax # 0x601038 >> <a> >> 0x0000000000400473 <+35>: and $0x3,%eax >> 0x0000000000400476 <+38>: mov %eax,0x200bc8(%rip) # 0x601044 >> <c> >> [...] >> >> As you can see both division and modulo was substituted with "shr" and >> "and". >> >> So basically nowadays there is no need to worry about that and >> complicate code with explicit low-level optimizations. Hope that >> answers your question. >> >> Regards, >> Andriy >> >> >> On Wed, Aug 23, 2017 at 4:15 PM, Pragash Vijayaragavan <pxv3...@rit.edu> >> wrote: >> > Hi, >> > >> > I got the chance to look at the cuckoo hash used in dpdk and have a >> > query. >> > >> > would using division and modulo operations be slower than bitwise >> > operations on RTE_HASH_BUCKET_ENTRIES, specially since >> > RTE_HASH_BUCKET_ENTRIES is a power of 2. >> > For example, to do a modulo we can do a "AND" operation on >> > (RTE_HASH_BUCKET_ENTRIES - 1), which might be faster. We did a cuckoo >> > filter for VPP and doing this gave a slight improvement in speed. >> > Is there any particular reason its done this way. >> > >> > Sorry if i am being wrong in any way, i was just curious. >> > >> > Thanks, >> > >> > Pragash Vijayaragavan >> > Grad Student at Rochester Institute of Technology >> > email : pxv3...@rit.edu >> > ph : 585 764 4662 >> >> >> >> -- >> Andriy Berestovskyy -- Andriy Berestovskyy