Re: Prioritizing Channel Access per Record?

[Brian Bevins <bevins@jlab.org>]

In the current iteration, the big ones are 65536 floats and there are 13 
of them. Much more data is available from the underlying hardware, and 
I'd like to get up to ~500K floats each if I can do it without choking 
all the other records.

Thanks,
--Brian

On 03/18/14 13:05, Mark Rivers wrote:
> Hi Brian,
>
> How big are your waveform records?
>
> Mark
>
> -----Original Message-----
> From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Brian Bevins
> Sent: Tuesday, March 18, 2014 11:27 AM
> To: tech-talk@aps.anl.gov
> Subject: Re: Prioritizing Channel Access per Record?
>
> On 03/18/14 12:03, Ralph Lange wrote:
> > On 18.03.2014 16:47, Brian Bevins wrote:
> > > Is there any way to specify that CA delivery of updates from certain
> > > records should be prioritized over other records on the same ioc?
> > >
> > > I've got an application where a bunch of ai's are processed at 10Hz
> > > and some relatively big (for us) waveforms are processed at about
> > > 0.3-0.5 Hz. The ioc is not heavily loaded and all record processing
> > > seems to happen in a timely way, but from the client end (EDM) the
> > > "fast" records all pause for ~0.5 sec whenever the waveforms push out
> > > their CA updates.
> > >
> > > The ai's are already being processed at a higher priority, but this
> > > doesn't seem to help their updates get pushed out with higher priority.
> > >
> > > Is there some tinkering I can do with the priorities of the CA
> > > threads to get what I want? How can I tell which thread will get
> > > which record updates? Is there something more obvious I'm missing?
> > >
> > > Thanks,
> > > --Brian
> > The CA thread pairs on the server (IOC) are created per client.
> > The client can set the priority as an argument to the
> > ca_create_channel() call [1].
> > If the client-set priorities are honored on the server depends on the
> > server side OS and/or configuration.
> >
> > On real-time Linux, the MCoreUtils module [2] (EPICS 3.15 only)
> > contains a rule-based engine to tinker with IOC thread priorities and
> > policies.
> >
> > Cheers,
> > ~Ralph
> >
> > [1]
> > http://www.aps.anl.gov/epics/base/R3-14/12-docs/CAref.html#ca_create_channel
> > [2] http://epics.sourceforge.net/mcoreutils/
> Thanks for the quick reply, Ralph.
>
> Using client-set priorities occurred to me, but then it seems I would
> need to write my own client to monitor and display the slow (or fast)
> records. Standard clients are all pretty much going to use a default
> priority in ca_create_channel(). If there is an existing general purpose
> client that allows setting the priorities, I'd love to hear about it.
> I'm currently using R3.14.12.3 on RTEMS, and I don't yet know if that
> supports client-set priority. If it does, then writing a little display
> program might work.
>
> If I were to switch to rt linux and make use of mcoreutils, it sounds
> like I would essentially run two virtual iocs on the same machine, one
> at a higher priority. Is that right?
>
> Thanks,
> --Brian


--
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