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List:       user-mode-linux-user
Subject:    Re: [uml-user] Emulating physical machines using UML?
From:       Jim Carter <jimc () math ! ucla ! edu>
Date:       2005-04-22 17:26:43
Message-ID: Pine.LNX.4.61.0504221014140.17158 () simba ! math ! ucla ! edu
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On Fri, 22 Apr 2005, Ragnar Lonn wrote:
> The problem here is that there can only be ~250 routing tables configured
> on the machine. This means that we can only emulate ~250 separate client
> machines (boxes with their own MAC addresses) on a single PC. We would
> like to emulate about 1000 separate client machines on one PC.

The testbed design is very interesting and I wish you luck with it.  
However, CPU's and memory don't multiply by magic, nor network bandwidth.  
I hope the client software uses few CPU cycles and the content is sparing 
of bandwidth.  Also, only one client at a time can bother the server, and 
the most interesting bugs will be race conditions when multiple clients hit 
the server simultaneously.

You certainly can use UML to host the clients, but you'll probably need 
several host boxes.  A multi-CPU motherboard could be helpful.  While 
hyperthread doesn't really multiply the CPU power, the possibility of 
multiple threads might be worth the expense of hyperthread processors.  You 
will want to max out the RAM on each host box, because if the clients 
thrash in and out of the giant swap file, it will slow them down and 
probably spoil the test.  Consider using a single readonly root filesystem, 
with a separate COW image overlaying it for each guest to write on.  That 
will minimize disc service issues on the host.

Good luck with the project!

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA  90095-1555
Email: jimc@math.ucla.edu    http://www.math.ucla.edu/~jimc (q.v. for PGP key)


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