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From: "Medvedkin, Vladimir" <vladimir.medvedkin@intel.com>
To: "Kinsella, Ray" <ray.kinsella@intel.com>,
	Thomas Monjalon <thomas@monjalon.net>,
	Syam Prasad N Pearson <syam.pearson@gadgeon.com>
Cc: "users@dpdk.org" <users@dpdk.org>, "dev@dpdk.org" <dev@dpdk.org>,
	"Wang, Yipeng1" <yipeng1.wang@intel.com>,
	"Gobriel, Sameh" <sameh.gobriel@intel.com>,
	"Richardson, Bruce" <bruce.richardson@intel.com>
Subject: Re: [dpdk-dev] Doubt regarding DPDK hash Library implementation
Date: Thu, 4 Nov 2021 17:39:50 +0100
Message-ID: <6c1c908e-6a9a-c50d-0fa3-be61770ef97c@intel.com> (raw)
In-Reply-To: <PH0PR11MB47769F949D7FD3273A0ABB48908D9@PH0PR11MB4776.namprd11.prod.outlook.com>

Hello,

On 04/11/2021 15:46, Kinsella, Ray wrote:
> I would guess it - I would say it is related to cache alignment.
> Assuming each entry is 8 bytes 😊
> 
> Ray K
> 
>> -----Original Message-----
>> From: Thomas Monjalon <thomas@monjalon.net>
>> Sent: Thursday 4 November 2021 14:12
>> To: Syam Prasad N Pearson <syam.pearson@gadgeon.com>
>> Cc: users@dpdk.org; dev@dpdk.org; Wang, Yipeng1
>> <yipeng1.wang@intel.com>; Gobriel, Sameh <sameh.gobriel@intel.com>;
>> Richardson, Bruce <bruce.richardson@intel.com>; Medvedkin, Vladimir
>> <vladimir.medvedkin@intel.com>
>> Subject: Re: [dpdk-dev] Doubt regarding DPDK hash Library
>> implementation
>>
>> +Cc hash lib maintainers
>>
>> 01/11/2021 11:55, Syam Prasad N Pearson:
>>> Dear Sir/Madam,
>>> I am a developer trying to get familiar with the DPDK hash library.
>> I
>>> tried to make and use a hash table successfully.
>>> During the development I came across a variable
>>>
>>> /** Number of items per bucket. */
>>> *#define RTE_HASH_BUCKET_ENTRIES 8*
>>>
>>> defined inside:
>>> dpdk-20.11.3/dpdk-stable-20.11.3/lib/librte_hash /rte_cuckoo_hash.h
>>>
>>> Why does the library take this value as *8*, is there any particular
>>> reason for this? what if it is 16,32... etc.
>>>

Yes, RTE_HASH_BUCKET_ENTRIES can be any power of 2.
The reason for choosing 8 is a tradeoff between performance and memory. 
When it is equal to 8, the sizeof(struct rte_hash_bucket) equal to 
RTE_CACHE_LINE_SIZE, thus, there are no gaps in memory between the hash 
buckets due to their alignment.

>>> I am using DPDK 20.11.3 LTS.
>>>
>>> Please help.
>>
>>
> 

-- 
Regards,
Vladimir

  reply	other threads:[~2021-11-04 16:40 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-01 10:55 Syam Prasad N Pearson
2021-11-04 14:11 ` [dpdk-dev] " Thomas Monjalon
2021-11-04 14:46   ` Kinsella, Ray
2021-11-04 16:39     ` Medvedkin, Vladimir [this message]
2021-11-04 16:49       ` Thomas Monjalon
2021-11-06 23:23         ` Syam Prasad N Pearson

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