RE: Is it possible to have deterministic SoftIOC (R3.14.12) on Linux

[<james.rowland@diamond.ac.uk>]

Hi

 

I’ve been using RT_PREEMPT on RHEL5.6 for a Ethercat bus scanner running at 1KHz. I built the RedHat MRG Kernel 2.6.24 RPMs from source (not sure if centos has these yet) using the default config.

 

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_MRG/index.html

 

http://ftp.redhat.com/pub/redhat/linux/enterprise/5Server/en/RHEMRG/SRPMS/

 

I also installed the rtctl RPM to configure kernel task priorities.

 

Using clock_nanosleep I get a maximum wakeup latency of 40us on a core duo server which seems quite good. On a Pentium 4 single core machine latency was much worse, with some outliers at 1ms.

 

I ran the control loop in a real time pthread, you can use

 

pthread_attr_setschedpolicy

pthread_attr_setschedparam

pthread_mutexattr_setprotocol

 

To set up FIFO scheduling, real time priority and priority inheritance mutexes.

I communicate with EPICS tasks using message queues built on these features.

 

James

 

 

 

 

 

 

 

 

 

 

 

From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Jimmy Johnson
Sent: 20 January 2011 00:17
To: tech-talk@aps.anl.gov
Subject: Is it possible to have deterministic SoftIOC (R3.14.12) on Linux

 

Hi

    I am planning on using a SoftIOC (R3.14.12) on Linux and will want to run a control loop (about 1000 lines of C code spread across a few custom records) deterministically at 100Hz. There will not be any other user applications, in addition to the IOC, running on the box. The hardware will most likely be a quad core or Core i7. My original plan was to use CentOS 5.5 which has a 2.6-18 kernel (quite old and with very few or none of the real-time work rolled into the mainline kernel) but I can go with the latest 2.6-37 kernel or a Real Time patched 2.6.33-RT30 if necessary.

 

Does anyone have any recent experience with something like this?

Is the preempt patch needed to support this?

Will EPICS support this out of the box or does it need to be tweaked in anyway?

I am assuming USE_POSIX_THREAD_PRIORITY_SCHEDULING should be set to YES?

 

Thanks

Jimmy

 

 

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