From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <bruce.richardson@intel.com>
Received: from mga02.intel.com (mga02.intel.com [134.134.136.20])
 by dpdk.org (Postfix) with ESMTP id D79C87F6D
 for <dev@dpdk.org>; Fri, 14 Nov 2014 11:43:43 +0100 (CET)
Received: from orsmga001.jf.intel.com ([10.7.209.18])
 by orsmga101.jf.intel.com with ESMTP; 14 Nov 2014 02:53:27 -0800
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.07,385,1413270000"; d="scan'208";a="607772646"
Received: from bricha3-mobl3.ger.corp.intel.com ([10.243.20.28])
 by orsmga001.jf.intel.com with SMTP; 14 Nov 2014 02:53:26 -0800
Received: by  (sSMTP sendmail emulation); Fri, 14 Nov 2014 10:53:25 +0025
Date: Fri, 14 Nov 2014 10:53:25 +0000
From: Bruce Richardson <bruce.richardson@intel.com>
To: Kamraan Nasim <knasim@sidebandnetworks.com>
Message-ID: <20141114105325.GB13232@bricha3-MOBL3>
References: <CAPrTskioYqu_aad7EeepyuYb-9wDZWDOWXQpdCrD5Yofom__vA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAPrTskioYqu_aad7EeepyuYb-9wDZWDOWXQpdCrD5Yofom__vA@mail.gmail.com>
Organization: Intel Shannon Ltd.
User-Agent: Mutt/1.5.23 (2014-03-12)
Cc: dev@dpdk.org, Yuanzhang Hu <YHu@sidebandnetworks.com>
Subject: Re: [dpdk-dev] Load-balancing position field in DPDK load_balancer
 sample app vs. Hash table
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
X-List-Received-Date: Fri, 14 Nov 2014 10:43:44 -0000

On Thu, Nov 13, 2014 at 01:29:32PM -0500, Kamraan Nasim wrote:
> Hello,
> 
> So i've borrowed some code from the DPDK Load balancer sample application,
> specifically the load balancing position(byte 29th) to determine which
> worker lcore to forward the packet to.
> 
> The idea is that flow affinity should be maintained and all packets from
> the same flow would have the same checksum/5-tuple value
> 
> worker_id = packet[load_balancing_field] % n_workers
> 
> Question is that how reliable is this load balancing position? I am tempted
> to use Hash tables but I think this position based mechanism may be faster.
> 
> How have people's experience with this been in general?
>

Using a modulus "%" operation will be far, far faster than doing a hash table
lookup, though obviously it is not as flexible. [If you have a power-of-two
number of workers, you can replace the "%" by "&", if you like to shave off
another few cycles].
As for reliability, I'm afraid it depends entirely on your application and what
field you pick as to whether it works for load balancing or not. 

/Bruce