Re: Prioritizing Channel Access per Record?

[Brian Bevins <bevins@jlab.org>]

Thanks Andrew. That really helped me nail it down.

It turns out that I was conflating two separate effects. Contrary to 
what I originally thought, there was a brief periodic CA hiccup for all 
clients when my long-running calculation thread ran with a priority just 
above the low end of CA. There was also a synchronized much larger slow 
down for any client that was monitoring both the fast records and the 
waveforms.

The first seems to be solved by dropping the calculation priority to 
just below CA. I was afraid that would be too low, but surprisingly the 
overall effect on the timing of the calcs is small.

The second is worked around by always spawning a separate client (EDM) 
to view the waveforms. Even though the CA client threads have equal 
priority, the fast records don't seem to get delayed.

Many thanks for all the helpful suggestions!

--Brian

On 03/18/14 16:43, Andrew Johnson wrote:
> Hi Brian,
>
> On 03/18/2014 02:57 PM, Brian Bevins wrote:
> > Hmm. When I run casr on my ioc, I get back one priority value per
> > client, not one per channel. And all of the priorities are currently
> > zero. Should this output look different if I were setting priority on a
> > per channel basis from the client?
> The CA client has to use a separate TCP connection to the server for
> each priority, so internally the server groups them by connection and
> hence by priority.
>
> For experimental purposes the caget and camonitor programs can be
> configured to use a particular priority (-p <prio> where <prio> is 0-99
> with 0 as the default & lowest priority). I would suggest setting up one
> camonitor of your waveform records with default priority and a second
> one with higher priority on the faster channels. If this resolves the
> stuttering it tells you that it's probably worth exploring this approach
> further.
>
> HTH,
>
> - Andrew


--
Brian S. Bevins, PE
Computer Scientist / Mechanical Engineer
Thomas Jefferson National Accelerator Facility

     "The urge to save humanity is almost always only a false-face
      for the urge to rule it."
                                     -- H. L. Mencken