Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Mon, 21 Nov 2005 09:26:49 -0700

> 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.

I am curious. Is it possible to specify scheduling priorities for threads,
even if process global strict FIFO scheduling of isn't permissible?

It is a very good idea I think to have some sort of prioritized scheduling
for the threads even if it isn't perfect. I know that UNIX can prioritize
time slicing of processes, but perhaps this can't yet be applied to
individual threads?

Jeff

> -----Original Message-----
> From: Marty Kraimer [mailto:[email protected]]
> Sent: Monday, November 21, 2005 8:29 AM
> To: [email protected]
> Subject: Re: priorities
> 
> 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