Experimental Physics and
Industrial Control System

Till Straumann <[email protected]> · Tue, 26 Nov 2002 14:03:56 -0800

Eric Norum wrote:

On Tuesday, November 26, 2002, at 02:25  PM, Marty Kraimer wrote:

At the EPICS meeting last week Till asked:

1) Could we declare a maximum priority for any component of base?
2) Why does iocsh run at epicsThreadPriorityMax?

Brief discussion.

1) sounds like a good request. How about

epicsThreadPriorityBaseMax = 91

2) I will assume that this was done to be like vxWorks, which runs the

vxWorks shell at highest priority. If iocsh runs at

epicsThreadPriorityBaseMax it seems like it should be OK. If a very

high prority application thread uses all the CPU time iocsh can't get

control but this is the applications problem.

 (2) -- I think we did this to ensure that you could still get some

response at the console even if some other task went insane and started

gobbling CPU cycles. With a strict priority-based scheduler like RTEMS

and vxWorks you'd have no possiblity of dealing with such tasks if the

shell were at a lesser or equal priority.

Correct - but this could only happen if the insane task had a priority >

91. However, if the user were to spawn a task with this high a priority,

he/she probably knew what he/she was doing: that task was probably

hard-rt critical and it was not tolerable to have it wait for whatever

was going on at the console.

IMO, clamping everyghing to < 91 with the shell running at 91 is safe

- no runaway (base) task can lock the console. However, the user still

has the option of doing really critical work at a higher priority, if

necessary - at the risk of having a locked-up system should such a task

run away, of course.

The benefit of leaving a range of priorities to the user IMO far

outweighs the possible damage.

-- Till

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System