Re: Changing EPICS general Purpose Thread's Priorities

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

Dear Odagiri san,

Long time no see, I am glad to see your message 🙂

> 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?

It is possible to modify thread priority after the launching process, even possible to modify the scheduling policy (ex, SCHED_OTERH to SCHED_FIFO, to the real-time priority).

Please, check up the followings:

I am using linuxRT - preempted rt patch for this example.

uname -a

Linux cpu-b084-pm01 4.14.139-rt66 #1 SMP PREEMPT RT Mon Sep 30 14:33:17 PDT 2019 x86_64 GNU/Linux

We can check up process id, parent id, thread id, rt-priority, start time, running time, and thread name with the following command.

ps -Leo pid,ppid,tid,rtprio,stime,time,comm

21994 21993 22010      - Mar23 00:00:00 tpg

21994 21993 22011      - Mar23 00:00:00 tpg

21994 21993 22209     59 Mar23 00:00:00 timerQueue

21994 21993 22210     59 Mar23 00:00:00 timerQueue

21994 21993 22212      - Mar23 00:00:00 tpg

21994 21993 22215      - Mar23 00:00:00 tpg

21994 21993 22216     10 Mar23 00:00:00 taskwd

21994 21993 22217     69 Mar23 00:00:00 timerQueue

21994 21993 22218     58 Mar23 00:01:39 cbLow

21994 21993 22219     63 Mar23 00:00:00 cbMedium

21994 21993 22220     70 Mar23 00:00:00 cbHigh

21994 21993 22221     50 Mar23 00:00:00 dbCaLink

21994 21993 22222     98 Mar23 00:12:35 tpgIrqPollingTa

21994 21993 22223     89 Mar23 00:04:02 tpgSoftPollingT

21994 21993 22224     50 Mar23 00:02:59 tpgBsaPollingTa

21994 21993 22225     10 Mar23 00:01:13 tpgRateMeasureP

21994 21993 22226     10 Mar23 00:02:07 tpgDiagnosticsT

21994 21993 22227     50 Mar23 00:02:40 bsaDrvPoll

21994 21993 22228     57 Mar23 00:00:13 timerQueue

21994 21993 22229     66 Mar23 00:00:00 scanOnce

21994 21993 22230     59 Mar23 00:00:00 scan-10

21994 21993 22231     60 Mar23 00:00:00 scan-5

21994 21993 22232     61 Mar23 00:00:01 scan-2

21994 21993 22233     62 Mar23 00:00:07 scan-1

21994 21993 22234     63 Mar23 00:00:14 scan-0.5

21994 21993 22235     64 Mar23 00:00:09 scan-0.2

21994 21993 22236     65 Mar23 00:00:18 scan-0.1

21994 21993 22237     56 Mar23 00:00:00 asCaTask

21994 21993 22238     16 Mar23 00:00:00 CAS-TCP

21994 21993 22239     12 Mar23 00:00:54 CAS-UDP

21994 21993 22240     14 Mar23 00:00:00 CAS-beacon

21994 21993 22241     51 Mar23 00:00:00 CAC-event

21994 21993 22242     10 Mar23 00:00:00 logRestart

21994 21993 22243     10 Mar23 00:00:00 caPutLog

21994 21993 22244     20 Mar23 00:00:24 save_restore

21994 21993 22245     10 Mar23 00:00:00 ipToAsciiProxy

21994 21993 22246     22 Mar23 00:01:42 timerQueue

21994 21993 22247     24 Mar23 00:00:27 CAC-UDP

21994 21993 22250     22 Mar23 00:00:04 CAC-event

21994 21993 22778     18 08:36 00:00:00 CAS-event

21994 21993 22779     20 08:36 00:00:00 CAS-client

22756  6877 22756      - 08:28 00:00:00 dropbear

The 3rd column is thread id, and the 4th column is a priority.  The symbol "-" means no rt-priority for the thread, SCHED_OTHER.

The thread "scan-10" has thread id 22230 and rt-priority 59.

The thread "CAS-TCP" has thread id 22238 and rt-priority 16.

If we want to escalate the rt-priority for those threads, we can do the followings:

# Escalate rt-priority of scan-10 to 60

chrt -f -p 60 22230

pid 22230's current scheduling policy: SCHED_FIFO

pid 22230's current scheduling priority: 59

pid 22230's new scheduling policy: SCHED_FIFO

pid 22230's new scheduling priority: 6

# Escalate rt-priority of CAS-TCP to 20

chrt -f -p 20 22238

pid 22238's current scheduling policy: SCHED_FIFO

pid 22238's current scheduling priority: 16

pid 22238's new scheduling policy: SCHED_FIFO

pid 22238's new scheduling priority: 20

Then, you can see the priorities of those two threads were escalated.

21994 21993 22229     66 Mar23 00:00:00 scanOnce

21994 21993 22230     60 Mar23 00:00:00 scan-10        <==========   59 to 60

21994 21993 22231     60 Mar23 00:00:00 scan-5

21994 21993 22232     61 Mar23 00:00:01 scan-2

21994 21993 22233     62 Mar23 00:00:07 scan-1

21994 21993 22234     63 Mar23 00:00:14 scan-0.5

21994 21993 22235     64 Mar23 00:00:09 scan-0.2

21994 21993 22236     65 Mar23 00:00:18 scan-0.1

21994 21993 22237     56 Mar23 00:00:00 asCaTask

21994 21993 22238     20 Mar23 00:00:00 CAS-TCP       <========= 16 to 20

21994 21993 22239     12 Mar23 00:00:54 CAS-UDP

21994 21993 22240     14 Mar23 00:00:00 CAS-beacon

I think the help message of the "chrt" will be helpful.

chrt --help

BusyBox v1.31.0 (2019-09-30 13:30:59 PDT) multi-call binary.

Usage: chrt -m | -p [PRIO] PID | [-rfobi] PRIO PROG [ARGS]

Change scheduling priority and class for a process

-m Show min/max priorities

-p Operate on PID

-r Set SCHED_RR class

-f Set SCHED_FIFO class

-o Set SCHED_OTHER class

-b Set SCHED_BATCH class

-i Set SCHED_IDLE class

Thank you.

Best regards,

Kukhee

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of jun-ichi.odagiri--- via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, March 26, 2021 12:09 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Changing EPICS general Purpose Thread's Priorities

 

Dear Han san,

Thank you for sending me the information.
I took a look at the site you have let me know.
But, I may be dense, I could not get the point.
It seems like that the information on the site is related
to Multi-Core Linux.

To be more concrete, I tell you what I have in my mind as
follows.

1. A Single-Core CPU is running Linux.
2. Only one IOC program is running on the Linux.
3. The IOC program is multi-threaded, as every one knows.

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?

Thanks a lot again in advance.

Best regards,

J.Odagiri at KEK. 


----- Original Message -----
> Jun-ichi Odagiri san,
>
> This may be what you are looking for.
>
> https://github.com/epics-modules/MCoreUtils
>
> Best,
> Han
>
>
> On Thu, Mar 25, 2021 at 4:55 PM jun-ichi.odagiri--- via Tech-talk
> <tech-talk at aps.anl.gov> wrote:
> >
> > Hi, all
> >
> > Do we have a way to change the priorities of the EPICS
> > general purpose threads dynamically on the iocsh？
> >
> > Thanks a lot in advance.
> >
> > Jun-ichi Odagiri(KEK)
> >
> >
> >
>