[pcp] PCP Network Latency PMDA

[Frank Ch. Eigler]

>> Its common for someone to run something like "pminfo -f network" to get
>> a high level look, then browse through the result, maybe iterating on
>> further with pminfo to something more specific, or switching to pmchart
>> or another tool for a different view.
>
> I think it's reasonable for such one-shot clients to suffer from the
> indignity of a PM_ERR_PMDANOTREADY for such metrics.  (That's not too
> surprising, considering that the semantics would probably be COUNTER,
> which are meaningless in isolation.)

By the way, it would not be a big stretch for the PMDA retain
collection of these statistics for some time after a PCP client
closes, in case of a reconnection soon by an equivalent context.
This way, even

     % pminfo -f papi.system.FOOBAR
     -ERR_NOTREADY
     % pminfo -f papi.system.FOOBAR
     12345
     % pminfo -f papi.system.FOOBAR
     23456

would work.

- FChE