[dpdk-dev] cuckoo hash in dpdk

[Dumitrescu, Cristian]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Pragash
> Vijayaragavan
> Sent: Wednesday, August 23, 2017 3:16 PM
> To: dev at dpdk.org
> Cc: Minseok Kwon <mxkvcs at rit.edu>
> Subject: [dpdk-dev] cuckoo hash in dpdk
> 
> 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 : pxv3620 at rit.edu
> ph : 585 764 4662

Bitwise AND typically takes 1 cycle on any CPU, while modulo takes dozens of cycles.