From: "Medvedkin, Vladimir" <vladimir.medvedkin@intel.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
"thomas@monjalon.net" <thomas@monjalon.net>
Cc: "Wang, Yipeng1" <yipeng1.wang@intel.com>,
"Stephen Hemminger" <stephen@networkplumber.org>,
"dev@dpdk.org" <dev@dpdk.org>,
"Morten Brørup" <mb@smartsharesystems.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"Ananyev, Konstantin" <konstantin.ananyev@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>,
nd <nd@arm.com>, nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH 0/3] add new Double Word Key hash table
Date: Wed, 1 Apr 2020 18:37:51 +0000 [thread overview]
Message-ID: <f75fb6f1004f4a389e7b1d55d71f1a87@intel.com> (raw)
In-Reply-To: <AM6PR08MB46449B65579E1FC656FDA2E698C80@AM6PR08MB4644.eurprd08.prod.outlook.com>
Hi Honnappa,
-----Original Message-----
From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Sent: Tuesday, March 31, 2020 10:17 PM
To: thomas@monjalon.net; Medvedkin, Vladimir <vladimir.medvedkin@intel.com>
Cc: Wang, Yipeng1 <yipeng1.wang@intel.com>; Stephen Hemminger <stephen@networkplumber.org>; dev@dpdk.org; Morten Brørup <mb@smartsharesystems.com>; dev@dpdk.org; Ananyev, Konstantin <konstantin.ananyev@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>; nd <nd@arm.com>; Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
Subject: RE: [dpdk-dev] [PATCH 0/3] add new Double Word Key hash table
<snip>
>
> 26/03/2020 18:28, Medvedkin, Vladimir:
> > Hi Yipeng, Stephen, all,
> >
> > On 17/03/2020 19:52, Wang, Yipeng1 wrote:
> > > From: Stephen Hemminger <stephen@networkplumber.org>
> > >> 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
>
> Yes some work is in progress to propose a new memory allocator for
> small objects of fixed size with small memory overhead.
>
>
> > >> 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.
> >
> > The main reason for this new hash library is performance. As I
> > mentioned earlier, the current rte_fbk implementation is pretty fast
> > but it has a number of drawbacks such as 2 byte values and limited
> > collision resolving capabilities. On the other hand, rte_hash
> > (cuckoo
> > hash) doesn't have this drawbacks but at the cost of lower
> > performance comparing to rte_fbk.
> >
> > If I understand correctly, performance penalty are due to :
> >
> > 1. Load two buckets
> >
> > 2. First compare signatures
> >
> > 3. If signature comparison hits get a key index and find memory
> > location with a key itself and get the key
> >
> > 4. Using indirect call to memcmp() to compare two uint32_t.
> >
> > The new proposed 4 byte key hash table doesn't have rte_fbk
> > drawbacks while offers the same performance as rte_fbk.
> >
> > Regarding use cases, in rte_ipsec_sad we are using rte_hash with 4
> > byte key size. Replacing it with a new implementation gives about
> > 30% in performance.
> >
> > The main disadvantage comparing to rte_hash is some performance
> > degradation with high average table utilization due to chain
> > resolving for 5th and subsequent collision.
rte_hash is linearly scalable across multiple cores for lookup due to lock-free algorithm. How is the scalability for the new algorithm?
This library is scalable as well. It uses almost the same lock-free algorithm. The only difference with cuckoo is that cuckoo in lock-free implementation uses single global "change_counter" for all the table, and the proposed implementation uses fine grained approach with "change_counter" per bucket. So it should be more scalable with frequent concurrent updates.
>
> Thanks for explaining.
> Please, such information should added in the documentation:
> doc/guides/prog_guide/hash_lib.rst
>
>
next prev parent reply other threads:[~2020-04-01 18:37 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-16 13:38 Vladimir Medvedkin
2020-03-16 13:38 ` [dpdk-dev] [PATCH 1/3] hash: add dwk hash library Vladimir Medvedkin
2020-03-16 13:38 ` [dpdk-dev] [PATCH 2/3] test: add dwk hash autotests Vladimir Medvedkin
2020-03-16 13:38 ` [dpdk-dev] [PATCH 3/3] test: add dwk perf tests Vladimir Medvedkin
2020-03-16 14:39 ` [dpdk-dev] [PATCH 0/3] add new Double Word Key hash table Morten Brørup
2020-03-16 18:27 ` Medvedkin, Vladimir
2020-03-16 19:32 ` Stephen Hemminger
2020-03-17 19:52 ` Wang, Yipeng1
2020-03-26 17:28 ` Medvedkin, Vladimir
2020-03-31 19:55 ` Thomas Monjalon
2020-03-31 21:17 ` Honnappa Nagarahalli
2020-04-01 18:37 ` Medvedkin, Vladimir [this message]
2020-04-01 18:28 ` Medvedkin, Vladimir
2020-03-16 19:33 ` Morten Brørup
2020-04-08 18:19 ` [dpdk-dev] [PATCH v2 0/4] add new k32v64 " Vladimir Medvedkin
2020-04-15 18:17 ` [dpdk-dev] [PATCH v3 " Vladimir Medvedkin
2020-04-15 18:51 ` Mattias Rönnblom
2020-04-16 10:18 ` Medvedkin, Vladimir
2020-04-16 11:40 ` Mattias Rönnblom
2020-04-17 0:21 ` Wang, Yipeng1
2020-04-23 16:19 ` Ananyev, Konstantin
2020-05-08 20:08 ` Medvedkin, Vladimir
2020-04-16 9:39 ` Thomas Monjalon
2020-04-16 14:02 ` Medvedkin, Vladimir
2020-04-16 14:38 ` Thomas Monjalon
2020-05-08 19:58 ` [dpdk-dev] [PATCH v4 0/4] add new kv " Vladimir Medvedkin
2020-06-16 16:37 ` Thomas Monjalon
2021-03-24 21:28 ` Thomas Monjalon
2021-03-25 12:03 ` Medvedkin, Vladimir
2023-06-12 16:11 ` Stephen Hemminger
2020-05-08 19:58 ` [dpdk-dev] [PATCH v4 1/4] hash: add kv hash library Vladimir Medvedkin
2020-06-23 15:44 ` Ananyev, Konstantin
2020-06-23 23:06 ` Ananyev, Konstantin
2020-06-25 19:56 ` Medvedkin, Vladimir
2020-06-25 19:49 ` Medvedkin, Vladimir
2020-06-24 1:19 ` Wang, Yipeng1
2020-06-25 20:26 ` Medvedkin, Vladimir
2020-06-25 4:27 ` Honnappa Nagarahalli
2020-05-08 19:58 ` [dpdk-dev] [PATCH v4 2/4] hash: add documentation for " Vladimir Medvedkin
2020-05-08 19:58 ` [dpdk-dev] [PATCH v4 3/4] test: add kv hash autotests Vladimir Medvedkin
2020-05-08 19:58 ` [dpdk-dev] [PATCH v4 4/4] test: add kv perf tests Vladimir Medvedkin
2020-04-15 18:17 ` [dpdk-dev] [PATCH v3 1/4] hash: add k32v64 hash library Vladimir Medvedkin
2020-04-15 18:59 ` Mattias Rönnblom
2020-04-16 10:23 ` Medvedkin, Vladimir
2020-04-23 13:31 ` Ananyev, Konstantin
2020-05-08 20:14 ` Medvedkin, Vladimir
2020-04-29 21:29 ` Honnappa Nagarahalli
2020-05-08 20:38 ` Medvedkin, Vladimir
2020-04-15 18:17 ` [dpdk-dev] [PATCH v3 2/4] hash: add documentation for " Vladimir Medvedkin
2020-04-15 18:17 ` [dpdk-dev] [PATCH v3 3/4] test: add k32v64 hash autotests Vladimir Medvedkin
2020-04-15 18:17 ` [dpdk-dev] [PATCH v3 4/4] test: add k32v64 perf tests Vladimir Medvedkin
2020-04-08 18:19 ` [dpdk-dev] [PATCH v2 1/4] hash: add k32v64 hash library Vladimir Medvedkin
2020-04-08 23:23 ` Ananyev, Konstantin
2020-04-08 18:19 ` [dpdk-dev] [PATCH v2 2/4] hash: add documentation for " Vladimir Medvedkin
2020-04-08 18:19 ` [dpdk-dev] [PATCH v2 3/4] test: add k32v64 hash autotests Vladimir Medvedkin
2020-04-08 18:19 ` [dpdk-dev] [PATCH v2 4/4] test: add k32v64 perf tests Vladimir Medvedkin
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