sPHENIX HCal discussion

[Martin Purschke <purschke AT bnl.gov>]

Dear all,

Abhisek and I had a longer (private) email discussion today how to go
about the online monitoring.

Since we switched to rcdaq as the data acquisition framework, we have
quite a number of amenities when it comes to accessing online data. For
veteran rcdaq users, this is not really new.

rcdaq provides a means to tap into an online stream and obtain, on a
best-effort basis, events for your monitoring. This is independent of
the files written to disk and also works if you are not actually logging
data and run the DAQ "dry". This is a convenient way to make some
adjustments in your setup without cluttering the disk with files, for
example if you adjust some HV until your signal is in the right spot. Of
course nothing prevents you from logging the data.

Good old pmonitor, which turned 16 recently, is a tool that lets you
monitor your data at the most interactive level if you so choose. You
can manipulate (display, reset, fit, what have you) histograms *while*
they are being filled in the background. Staying with the HV-adjustment
example, you could reset the histogram you are looking at after each
change of the HV and only see the latest entries with the new HV setting.

Many Phenixians have only ever seen the "billboard-style" monitoring
pages we have in 1008. They are not actually interactive in the sense
that you cannot manipulate them; you get to see pre-arranged root
canvases with histograms from the current data. The monitoring setup we
have in 1008 is not exactly lightweight, but it does allow multiple
instances of the same canvases being shown. For example, the DM can look
at things, and I can look at that at home at the same time (and we cycle
through the pages on the overhead monitor).

You can get the same behavior from pmonitor, of course. However, for the
test beam, I'd like to move those "billboard-style", static and
pre-arranged monitoring pages to the web browser entirely. This has the
advantage that you can conveniently monitor your data from anywhere as
long as you can reach the web server.

To show how (and that) this works, I am running a pretend-HCal pmonitor
process on the hcaldaq machine right now. It is really running the
ready-made "p_ex2" pmonitor example project that ships with the
distribution. The example gets events from the test stream and uses that
stream's packet 1003 to fill two histograms with random values.

In order to see the page, you need to establish a tunnel from your local
port 10290 to hcaldaq's port 8085 - for this example to work, you *must*
use those numbers.

e.g.

ssh -L 10290:hcaldaq:8085 highbaygw.phy.bnl.gov

(this tunnel is no different from the one you set up to get to the
Highbay's Elog server - except for the port numbers, of course).

Then go here:

http://www.phenix.bnl.gov/~purschke/monitoring/monipage1.html

In addition to some text, you see the two histograms in 2 different
views each. I made the page automatically refresh itself every 10s, and
you will see that the histograms actually change each time.

Except for the fact that this is reading a test stream, this is real
online monitoring running in the Highbay. When the DAQ is running, we
could just as well read the rcdaq online stream and get a similar,
yet-to-be-made page (or multiple pages) with the hcal-specific
monitoring histograms. It is also possible to give some level of
interactivity to the page by way of buttons (e.g. reset the histograms).


You open the online stream with
rcdaqopen("hostname");
in pmonitor, and with
dlist -r ...
or
ddump -r ...
with the standard tools. (dpipe has not been updated yet, on the list).
"hostname" defaults to "localhost", so on the local machine where rcdaq
is running, one can just rcdaqopen();.

There is one small - temporary - caveat. There is a regression from the
older versions of rcdaq and pmonitor. The change improves the resilience
of the pair when one simply kills one or the other while the online
stream is being read. However, a side effect that came to light only
recently is that right now only one process can read the online stream
at a time. This worked before for an arbitrary number of concurrent
clients, and I will get this behavior back as soon as I can. It is very
convenient to be able to look at a few events from the DAQ with "ddump
-r ...". Stay tuned.

For now, make the tunnel and have a look at the page. I attach a partial
screenshot just in case.

   Martin

-- 
Martin L. Purschke, Ph.D.        ;   purschke AT bnl.gov
                                 ;   http://www.phenix.bnl.gov/~purschke
                                 ;
Brookhaven National Laboratory   ;   phone: +1-631-344-5244
Physics Department Bldg 510 C    ;   fax:   +1-631-344-3253
Upton, NY 11973-5000             ;   skype: mpurschke
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