Experimental Physics and
Industrial Control System

"jun-ichi.odagiri--- via Tech-talk" <tech-talk at aps.anl.gov> · Tue, 30 Mar 2021 11:55:23 +0900

Dear Ralph,

I assume that "you" means me in your message because I
triggered this chain of e-mails. If not, please just ignore
this e-mail.

(I know "you" can mean unspecified persons in English.)

What I wanted to do was to give "CAS-client" a priority
higher than that of "scan-0.1" because commands sent from
a CA client to an IOC start to be lost when the number of
records being processed with the SCAN value of ".1 seconds"
was increased.

But now I understand that the problem of mine is not an
issue of priorities of threads but an issue of something
else.

(I think default priorities of the EPICS IOC threads
are well-chosen as you mentioned in a previous e-mail.)

I do not want to choose multiple IOCs solution because
I want to keep the system as simple as possible.

The value of PRIO field is irrelevant because I do not
rely on callback threads in my device support.

I can not choose multiple parallel callback solution
because my system is single-CPU system.

I now suspect that the origin of my problem is not on
IOC-side but on a custom device-side being controlled
by the IOC.

Lots of thanks anyway for your detailed comments and
advice.

Best regards,

J.Odagiri at KEK

----- Original Message -----
> So, coming back to what (I think) was the original question:
> How to change the priority of the general purpose callback threads (
named
> "cb...") to be higher than a periodic scanning thread?
> 
> You don't have to. Use the PRIO field.
> There are three (sets of) general purpose callback threads, related to 
the
> three values of the records' PRIO field: Low, Medium and High.
> Their priorities are designed to be lower than all periodic processing
> (Low), halfway between the slow and the fast periodic processing (
Medium)
> and higher than all period processing (High). For each record, the 
thread
> used for callback processing is selected based on the setting of its 
PRIO
> field.
> On multi-CPU systems, you can also enable multiple parallel callback
> threads (e.g., one per CPU) to boost the callback and 'I/O Intr' 
processing
> power of your IOC.
> 
> Only if these mechanisms show not being sufficient for your 
application,
> additional steps need to be taken. In most cases, I would assume 
further
> parallelization (splitting up the application to multiple IOCs, adding 
more
> CPU power) to be more efficient than tuning priorities.
> 
> Cheers,
> ~Ralph
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System