Re: Changing EPICS general Purpose Thread's Priorities

[William Layne via Tech-talk <tech-talk at aps.anl.gov>]

A few other ideas is that you can try multiple callback threads or splitting into multiple IOCs.

On Sat, Mar 27, 2021, 2:32 AM jun-ichi.odagiri--- via Tech-talk <tech-talk at aps.anl.gov> wrote:

Dear Ralph

Thanks for your reply.

> Changing priorities of callback, driver or communication threads with
> respect to database processing.
>
> Which is exactly what your question is about.

I got it. Thanks!

> Why do you want to change the priority of "CAS-TCP"? Note that this is
not
> a "general purpose thread", but one of the core threads of the Channel
> Access server.

Here is the reason.

An IOC controls many power supplies of something. The IOC is polling the
status of the power supplies at a SCAN rate of 0.1 seconds. When the
number of the power supplies increases, the IOC starts to lose commands
sent from an CA-client. I thought that the problem would be solved if
I give the "CAS-TCP" a priority which is higher than that of "scan-0.1".


But, on the second thought, I realized that there is no need to do that
because the commands sent from the CA-client will be queued on the IOC-
side.
As far as some time is left for the "CAS-TCP" to run, the loss of
commands
should not occur.

Am I right?

I guess the origin of the problem would not be an issue of priority but
an issue of throughput. So, I decided to solve the problem by improving
the efficiency of the polling of the status of the power supplies.
Fortunately, there is a way to do that.

>     The default priorities of the EPICS IOC threads are well-chosen.
They
> have been proven to ensure reliable IOC operation and communication,
in
> many installations, under a variety of circumstances.

I am really aware of this. That is the reason why I noticed my
misunderstanding
of the situation.

Best regards,

J.Odagiri at KEK


----- Original Message -----
> On Fri, 26 Mar 2021 at 08:09, jun-ichi.odagiri--- via Tech-talk <
> tech-talk at aps.anl.gov> wrote:
>
> > Here is my question.
> >
> > Can I change the priority of "CAS-TCP" thread and "scan-10"
> > thread so that the former is given a higher priority than
> > that of the latter without modifying any source files in
> > base?
> >
> > Does the site you guided me to answer the question?
> >
>
> As per the README of the MCoreUtils, one of its features is
>
> Changing priorities of callback, driver or communication threads with
> respect to database processing.
>
> Which is exactly what your question is about.
>
> The MCoreUtils facility allows rule-based manipulation of thread
> properties, so that things like changing a priority will apply to all
> threads with a name matching a specific pattern, whenever they will be
> created on that IOC.
>
> Why do you want to change the priority of "CAS-TCP"? Note that this is
not
> a "general purpose thread", but one of the core threads of the Channel
> Access server.
> (From the MCoreUtils documentation:)
> Warning
>     The default priorities of the EPICS IOC threads are well-chosen.
They
> have been proven to ensure reliable IOC operation and communication,
in
> many installations, under a variety of circumstances.
>     Manipulating the real-time properties, especially scheduling
policies
> and priorities, may have unwanted side effects. Use this feature
sparingly,
> and test well.
>
> Cheers,
> ~Ralph
>