Re: Question on Multiple Instruments in one IOC or Multiple IOCs for each

["Hu, Yong via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Adam,

 

Since you are using Debian flavors, you may take a look at the Debian package “sysv-rc-softioc” which wraps procServ to manage multiple IOCs on a host. I usually run tens of IOCs (or about 100 IOCs) on a ~$4K Linux server.

https://epicsdeb.bnl.gov/debian/

 

If you have difficulty installing the Debian package “sysv-rc-softioc” above, you may try the tool I recently developed below which is generic for all systemd-based Linux (Debian, RedHat, …).

(systemd-style scripts for procServ with the intent of running an EPICS IOC):

https://github.com/NSLS-II/systemd-softioc

 

Q:“What is the difference between spawning multiple IOCs through running your st.cmd for each and instead spawning them using procServ?”

A: Yes, you can simply type “./st.cmd &” in a terminal to start an IOC (or use tools such as screen, tmux, nohup to start an IOC). I tried all of these methods when I was a graduate student decades ago. But I like “procServ” the most (especially the Debian package “sysv-rc-softioc” which was originally developed by Michael Davidsaver) after I started my first job at NSLS-2. Since “sysv-rc-softioc” or “systemd-softioc” is a piece of software and it has some strict directory structure requirements, you need to learn how to use it properly. Once you know how to use all kinds of tools, you will know the difference and you will pick up the tool which is most comfortable for yourself.

 

Take your time to try sysv-rc-softioc (or systemd-softioc) and you will not regret spending your time on it.

 

Good luck!

Yong

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Reply-To: "Manoussakis, Adamandios" <manoussakis1 at llnl.gov>
Date: Tuesday, March 30, 2021 at 6:02 PM
To: "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Subject: RE: Question on Multiple Instruments in one IOC or Multiple IOCs for each

 

Hey Dave,

 

Thanks for the information, for platform we will be using Debian flavors of linux as the host for the IOCs and so far have not encountered running multiple IOCs of the epics 3/7.  I was concerned with spawning out so many IOC instances if I did go with the design of one ioc one device (looking at say 30+ IOCs on one host vs combining down to ~5).  I can see the benefit of efficiency when records need to communicate between each other but in this case the digitizers/dmms do not have any dependencies on each other. 

 

Couple other thoughts

 

I was looking at starting to use procServ but was a little confused from reading about the documentation on its use.  What is the difference between spawning multiple IOCs through running your st.cmd for each and instead spawning them using procServ?  Is the IOC treated differently in linux when using procServ to start them?

 

Will I run into resource issues (on a highend desktop) spawning so many IOCs (~30) on one host (I did implement Ralphs script already to solve the multiple ioc ca issue)?

 

Are there concerns when running say 8 devices using streamdevice in a single IOC, I would assume there might be some delay when streamdevice has to make multiple calls in the same IOC?

 

 

From: D Willimoto <dwilliams at kiesbar.com>
Sent: Tuesday, March 30, 2021 1:52 PM
To: Manoussakis, Adamandios <manoussakis1 at llnl.gov>
Subject: Re: Question on Multiple Instruments in one IOC or Multiple IOCs for each

 

Hi Adam,

 

The platform is one dependency.  Some platforms have trouble instantiating multiple IOCs of certain EPICS versions.  It's difficult to do on a RaspPi for instance.

 

I use RaspiPi to connect to a vacuum and power supply system and I combine them into one IOC for this reason.

 

From a design perspective, there are two contrary forces.  First, encapsulation of device as an object and address.  

 

Second is the power of records to be actions and perform modifications.  For instance a record can be a calculation from two other records. If so, you want those two source records in the same IOC to eliminate constant communication lag.  This factor also exists with other database systems like Elastic, Splunk, etc.

 

There are other perspectives but these are the main practical ones in my view.

 

Best,

Dave

 

 

On Wed, Mar 31, 2021 at 5:44 AM Manoussakis, Adamandios via Tech-talk <tech-talk at aps.anl.gov> wrote:

Hello,

 

From a design perspective, is it better to have one device per IOC or would it be more efficient to group same devices into one IOC?  I have multiple same instruments (digitizers, DMMs) and was thinking to create one IOC with say 8 Digitizers or 8 DMMs but wasn’t sure if this was the way to go about this.  If its better to go the other direction 1 device 1 IOC, is there a better way to spawn out the IOCs (I would guess a bash script with variables for any of the values that need to be changed eg. IP address for each)?

 

Thanks,

Adam