Experimental Physics and
Industrial Control System

"Steven M. Hartman" <[email protected]> · Mon, 23 May 2011 12:18:14 -0400

Dirk Zimoch wrote:

First incident:

An IOC (vxWorks 5.5) lost CA connectivity. All medm panels went white.

Logging in on the IOC over serial port showed that the data base was

still running, but there were many messages

"rsrv: system low on network buffers - send retry in 15 seconds"

These messages made it a bit tough to debug, because they spill all over

any output of any debug tool.

As you saw, mbuf starvation is usually recoverable once the client

starts behaving. Jeff's comments about queuing theory show that you

cannot protect the server completely, but you can hopefully tune

your buffer numbers to deal with most situations your network is

likely to experience. Was this a one-time event, and if so, was

anything unusual happening at the time? Which EPICS version for IOC

and the clients?

Second incident:

An other IOC lost CA connectivity. This time the error message was

different:

CA beacon (send to "...") error was "ENOBUFS"

This one is similar to what SNS has seen over the years with mv2100

and related boards with the DEC network driver. The precipitating

event is a temporary loss of the physical network layer (i.e.

unplugged network cable to IOC, or edge network switch powered

down). It looks like a buggy network driver that cannot recover from

this fault when there are lots of UDP packets queuing in the

outgoing buffers. This one does not seem to be recoverable except by

a reboot so we have taken steps to reduce the likelihood of loosing

the physical link. We do not see this with other boards.

--
Steven Hartman
[email protected]

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System