MBUF Cluster Network freeze problem

bob bobwis at ascweb.co.uk
Tue Nov 28 09:44:56 UTC 2000


I have come up against an interesting problem when the local BSP is
moderately task loaded and the local network is also very active talking to
the BSP. We are using the Mot 68360 and RTEMS 4.5 Beta
The symptoms are that the MBUF Clusters fill up slowly over time - as if the
CPU can't keep up with the processing of the data. Eventually, the message
"Still waiting for mbuf cluster." pops out from m_clalloc in rtems_glue.c.
If the other network traffic to the BSP is stopped, to reduce the external
network load to virtually nothing, the BSP still never recovers and seems to
have a no free clusters for ever (still has plenty of free MBUFS).

To generate this condition we run our normal applications - a PC which polls
a task in the BSP and a flood ping aimed at the BSP. It takes up to a couple
of minutes to fall-over. However, we think a similar situation may have
occurred in real life without needing the flood pings.

I believe the network should recover and the MBUF Clusters should free up
after the load is reduced.

Anyone got any theories on what's happening, or ideas on where to start
looking / work-arounds. I believe increasing MBUFs/Clusters will do no good
as I think it's the CPU overload, that causes them to fill up.

What we need is a graceful recovery?
Any help/ideas much appreciated, thanks.

Bob Wisdom




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