Experimental Physics and
Industrial Control System

Marty Kraimer <[email protected]> · Mon, 21 Nov 2005 09:29:25 -0600

Jeff Hill wrote:

Pursuing this a bit further, I notice, using epicsThreadShowAll, that the

OSI => OSD priority mapping maybe isn't working on POSIX (the OSSPRI

column

is always zero)?

Again, this is building with USE_POSIX_THREAD_PRIORITY_SCHEDULING = YES.

Two "features" of priority scheduling on linux.

1) On linux you must be running as root in order to be able to set

SCHED_FIFO.

 The code is written to silently revert to non-priority scheduling if

EPERM is returned.

2) Older versions of linux (perhaps all 2.4 versions without special

patches) do not seem to support priority scheduling. The implementations

seem to just silently ignore the priority scheduling requests even

though _POSIX_THREAD_PRIORITY_SCHEDULING is defined.

This it seems that the only way to know if priority scheduling is being

used is to run epicsThreadShowAll and see if the OSS prioritys have non

zero values.

Note that solaris shows non-zero values WITHOUT being root. When I run

top, I notice that the LWP has higher values than other processes. I do

not know how solaris is managing the priorities.

Marty

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System