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Re: GigE (was Re: [Discuss-gnuradio] DSP based SDR)

From: David Young
Subject: Re: GigE (was Re: [Discuss-gnuradio] DSP based SDR)
Date: Wed, 22 Jun 2005 18:22:34 -0500
User-agent: Mutt/1.4.1i

On Wed, Jun 22, 2005 at 12:40:06PM +0200, Harald Welte wrote:
> On Tue, Jun 21, 2005 at 04:10:35PM -0700, John Gilmore wrote:
> > What thruput do YOU see using a good GigE card under Linux?  Can you move
> > 100 Mbytes/sec from user process to user process with TCP, across two GigE
> > interfaces and a GigE switch?  If so, it's doing much better than USB2
> > ever will, and much better than any version of FireWire.
> I'm usually not doing client-to-server TCP benchmarks over my test
> networks, since I'm more interested in small-packet forwarding
> performance.  I'm sure with the right tuning (and probably some of the
> recent work on TCP BIC etc.) you can saturate a 1000-base-tx link with a
> single tcp flow, no question on that. 
> But at what expense?  you copy data back and forth between different
> address spaces (kernel/user), you have lots of complex code that deals
> with retransmissions, protocol demultiplex, ... that is totally
> unneccessarry for the gnuradio/USRP kind of application.

Systems like NetBSD have moved to "zero-copy" TCP.  I am surprised if
Linux has not done the same.  Perhaps more important is that I do not
see any reason, in principle, that you cannot do the same for UDP+RTP.
(API adaptations may be necessary.)


David Young             OJC Technologies
address@hidden      Urbana, IL * (217) 278-3933

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