Experimental Physics and
Industrial Control System

Di Maio Franck <[email protected]> · Mon, 26 Sep 2011 06:19:41 +0200

Dear base maintainers and Linux users

For ITER, we'll need to be able to tune the RT behavior of the control application for  RHEL and RHEL-MRG on multi-core platforms. 
This means not only controlling the threads' priority and the scheduling policy but also the threads' "CPU affinity" (distribution to given sub sets of the cores).

Cosylab provided us with a proposal for configuring these parameters either with the IOC shell or with system commands by naming the IOC threads. 
It implies some extensions in the code that have been prototyped already (code / patch available).

It is also proposed to change the EPICS-POSIX mapping to have the EPICS priorities 0 and 1 mapped to priority 1 and the other priorities equal.

The changes consist in:
1) 2 new commands: epicsThreadSetPosixPriority and epicsThreadSetPosixPriorityByName to set the priority and scheduling policy of a thread.
2 ) 2 new commands: epicsThreadSetCPUAffinity and epicsThreadSetCPUAffinityByName to set the CPU affinity of a thread.
3) Extensions of the epicsThreadShow and epicsThreadShowAll to add lightweight process ID, scheduling policy and CPU affinity
4) An extension to allow the Linux thread to have the EPICS name in their status (via the Linux prctl function).
5) A change in the POSIX priority mapping (have EPICS prio 0 and 1 mapped to POSIX 1 and all other identical).

A technical note describing these changes is available on the Cosylab site: 
	http://pub.cosylab.com/EPICS/EPICS_Real_Time.pdf

As well as the patches for prototyping these changes on 3.1.4.2:
	http://pub.cosylab.com/EPICS/epics-affinity-patch.txt

It would be nice to discuss this at the next collaboration meeting.

Franck Di Maio / ITER
Klemen Zagar / Cosylab

---
Franck Di Maio
CODAC System Designer
CODAC Section

ITER Organization, Building 519/027, CHD, Control System Division
Route de Vinon sur Verdon - 13115 St Paul Lez Durance - France

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System