Re: [dpdk-dev] [PATCH 0/3] add new Double Word Key hash table

["Wang, Yipeng1" <yipeng1.wang@intel.com>]

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Monday, March 16, 2020 12:33 PM
> To: Medvedkin, Vladimir <vladimir.medvedkin@intel.com>
> Cc: Morten Brørup <mb@smartsharesystems.com>; dev@dpdk.org;
> Ananyev, Konstantin <konstantin.ananyev@intel.com>; Wang, Yipeng1
> <yipeng1.wang@intel.com>; Gobriel, Sameh <sameh.gobriel@intel.com>;
> Richardson, Bruce <bruce.richardson@intel.com>; Suanming Mou
> <suanmingm@mellanox.com>; Olivier Matz <olivier.matz@6wind.com>;
> Xueming(Steven) Li <xuemingl@mellanox.com>; Andrew Rybchenko
> <arybchenko@solarflare.com>; Asaf Penso <asafp@mellanox.com>; Ori Kam
> <orika@mellanox.com>
> Subject: Re: [dpdk-dev] [PATCH 0/3] add new Double Word Key hash table
> 
> On Mon, 16 Mar 2020 18:27:40 +0000
> "Medvedkin, Vladimir" <vladimir.medvedkin@intel.com> wrote:
> 
> > Hi Morten,
> >
> >
> > On 16/03/2020 14:39, Morten Brørup wrote:
> > >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Vladimir
> > >> Medvedkin
> > >> Sent: Monday, March 16, 2020 2:38 PM
> > >>
> > >> Currently DPDK has a special implementation of a hash table for
> > >> 4 byte keys which is called FBK hash. Unfortunately its main
> > >> drawback is that it only supports 2 byte values.
> > >> The new implementation called DWK (double word key) hash supports 8
> > >> byte values, which is enough to store a pointer.
> > >>
> > >> It would also be nice to get feedback on whether to leave the old
> > >> FBK and new DWK implementations, or whether to deprecate the old
> one?
> > > <rant on>
> > >
> > > Who comes up with these names?!?
> > >
> > > FBK (Four Byte Key) and DWK (Double Word Key) is supposed to mean
> the same. Could you use 32 somewhere in the name instead, like in int32_t,
> instead of using a growing list of creative synonyms for the same thing?
> Pretty please, with a cherry on top!
> >
> >
> > That's true, at first I named it as fbk2, but then it was decided to
> > rename it "dwk", so that there was no confusion with the existing FBK
> > library. Naming suggestions are welcome!
> >
> > >
> > > And if the value size is fixed too, perhaps the name should also indicate
> the value size.
> > >
> > > <rant off>
> > >
> > > It's a shame we don't have C++ class templates available in DPDK...
> > >
> > > In other news, Mellanox has sent an RFC for an "indexed memory pool"
> library [1] to conserve memory by using uintXX_t instead of pointers, so
> perhaps a variant of a 32 bit key hash library with 32 bit values (in addition to
> 16 bit values in FBK and 64 bit in DWK) would be nice combination with that
> library.
> > >
> > > [1]: http://mails.dpdk.org/archives/dev/2019-October/147513.html
> > >
> > >
> > > Med venlig hilsen / kind regards
> > > - Morten Brørup
> > >
> 
> Why is this different (or better) than existing rte_hash.
> Having more flavors is not necessarily a good thing (except in Gelato)
 [Wang, Yipeng]
Hi, Vladimir,
As Stephen mentioned, I think it is good idea to explain the benefit of this new type of hash table more explicitly such as
Specific use cases, differences with current rte_hash, and performance numbers, etc.