Xen devel - Feb 2005 - XEN problems when using large # of NICs in domain U

I am trying to test XEN with a large # of NICs in domain U.  I configured a
single domain U to have 128 NICs (by simply setting the # of NICs to 128 in the
domain U configuration file). When I try to create the domain using "xm
create domainU -c", the domain starts to boot but then hangs when it
reaches the stage of initializing the virtual NICs (xen_net: Initialising
virtual ethernet driver).  After about 30 seconds, the machine reboots on its
own.
 
If I set the # of NICs to 512, domain U does not boot and instead I get the
following error message from xm: "Error: Callback timed out".  The
machine does not reboot in this case.
 
The magic number appears to be 122 - I can set the # of NICs to 122 and domain U
boots with no problems.  If I go to 123, it hangs and reboots my machine.  I can
also configure 2 domain U''s each with 61 NICs and that works fine. 
However if I increase one of them to 62 that domain fails to start and my
machine reboots (so the total is 123).  This also implies that the maximum # of
domain U''s possible on one machine is 122.
 
This does not appear to be a problem with the bridge - I did a little debugging
and it turns out that in all cases XEN sucessfully instantiates the back-end
network drivers and adds them to the bridge (all VIFx.y interfaces are visable
and registered with the bridge).  This could be a problem with the front-end
network drivers. I don''t see any failure debug ouput in any of the XEN
logs.
 
I tried all tests on 3 different physical machines with different amounts of
memory.  The domain U''s were configured with different amounts of
memory (from 64MB to 512MB).  This does not appear to be a memory issue.
 
Has anyone else tried this or have any other information on why this may be
occuring?
 
Eric
 

		
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