[uml-devel] tipc in networked UML

["Randy Macleod" <macleodr@nortelnetworks.com>]

Hello,

    I'm simulating a small cluster of processors using
UML (user-mode-linux.sourceforge.net)
and TIPC (tipc.sf.net).
Has anyone else tried this?

The network is simulated using tun devices, i.e.

cpu0 with eth0 in a UML is connected to pce.0.0.0
cpu1 with eth0 in a UML is connected to pce.0.1.0

A bridge device connects these pce(s) and forwards
ethernet frames based on mac addrs. Packet delivery
is communicated to the UML receiver by a signal according
to Jeff Dike (the UML guy)

Below is some output of /sbin/ifconfig -a on the desktop...

Now when these UML's load, a tipc kernel module gets insmod'ed
and things work to first order as expected.
BUT...
Several problems occur:

1. Connectionless communication is very unreliable.
   (see my previous post for tfsend/tfrecv))
   Only 100's of messages can be exchanged before getting
   a sequence error.

2. Resetting 1 node causes confusion of the tipc name table
of other nodes.

If I have 3 UML's (A,B,C),
  - publish a tipcname on A,
  - reset node C
  - then node A get stuck periodically withdrawing the published name.


3. On a lightly loaded system with 10s of processes per UML,
    there are frequently very long (> 5 seconds) tipc packet latencies
    whereas the normal latency is 0.3 seconds. The desktop load
    is always very low. If I ping each node every 0.1 seconds
    the high latencies mostly go away. Seem's like the signal
    is missed...

So, does TIPC assume real-time behaviour
of packets on the network. i.e. by the time N packets have been
sent, the other kernels have received the packets and will send
flow control messages?

If this is the case then I think a minimal modification to UML
to do a sched_yield() every N packets (in or out) would
help matters. Furthermore, it may be a good idea to co-operatively
schedule all the UML's so that their clocks are all in sync and
no node can send or receive too many packets at one time.

Comments?

// Randy




cpbr.0    Link encap:Ethernet  HWaddr 00:FF:3A:1A:CB:69
           inet addr:10.0.254.1  Bcast:10.255.255.255  Mask:255.255.0.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:52 errors:0 dropped:0 overruns:0 frame:0
           TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:1624 (1.5 Kb)  TX bytes:704 (704.0 b)

pce.0.0.0 Link encap:Ethernet  HWaddr 00:FF:E2:5D:50:B0
           UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
           RX packets:3262 errors:0 dropped:0 overruns:0 frame:0
           TX packets:2562 errors:0 dropped:149 overruns:0 carrier:0
           collisions:0 txqueuelen:1024
           RX bytes:452010 (441.4 Kb)  TX bytes:519063 (506.8 Kb)

pce.0.1.0 Link encap:Ethernet  HWaddr 00:FF:3A:1A:CB:69
           UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
           RX packets:6 errors:0 dropped:0 overruns:0 frame:0
           TX packets:1333 errors:0 dropped:1079 overruns:0 carrier:0
           collisions:0 txqueuelen:1024
           RX bytes:228 (228.0 b)  TX bytes:302530 (295.4 Kb)





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