Message-ID: <47586E7F.1020903@nortel.com>
Date: Thu, 06 Dec 2007 15:49:51 -0600
From: "Chris Friesen" <cfriesen@nortel.com>
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To: Andi Kleen <andi@firstfloor.org>
CC: Renzo Davoli <renzo@cs.unibo.it>, linux-kernel@vger.kernel.org
Subject: Re: New Address Family: Inter Process Networking (IPN)
References: <20071205164055.GA2082@cs.unibo.it> <p73bq94k8yd.fsf@bingen.suse.de> <20071206053016.GA1464@cs.unibo.it> <20071206163538.GC20595@one.firstfloor.org> <47585D66.3000404@nortel.com> <20071206212644.GA26725@one.firstfloor.org>
In-Reply-To: <20071206212644.GA26725@one.firstfloor.org>
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Andi Kleen wrote:
>>Latency was very 
>>important, so we ended up doing essentially a multicast unix socket 
>>rather than taking the extra penalty for UDP multicast.
> 
> 
> What extra penalty? Local UDP shouldn't be much more expensive than Unix.

On a 1.4GHz P4 I measured a 44% increase in latency between a unix 
datagram and a UDP datagram.

For UDP it has to go down the udp stack, then the ip stack, then through 
the routing tables and back up the receive side.

The unix socket just hashes to get the destination and delivers the message.

Chris
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