Re: Priorities of epicsThreads on Linux

[Andrew Johnson <anj@aps.anl.gov>]

Hi Jun-ichi,

On Wednesday 22 April 2009 07:47:51 jun-ichi.odagiri@kek.jp wrote:
>
> Thank you very much for the information.
>
> Just say "YES"...
> Is that all what I have to do?

Well, almost.  Linux only allows processes to use the pthreads real-time 
priorities if the process is sufficiently privileged (because it's easy to 
code a Denial of Service attack to bring down the OS if you have that 
privilege).  There's probably a Capability (CAP_xx) that controls this, but I 
don't know what it is.  The easiest way to provide that is to run the IOC as 
root, which I don't recommend on a general-use system for security reasons 
but should be Ok on a dedicated machine.

There is a test program called epicsThreadPriorityTest that you can run from 
your base/src/libCom/test/O.<arch> directory which tells you whether the 
threads are being scheduled strictly by priority or not, so you should be 
able to use that to experiment.

HTH,

- Andrew

> ----- Original Message -----
>
> > jun-ichi.odagiri@kek.jp wrote:
> > > Dear All;
> > >
> > > I've recently come to notice that the real-time performance of Linux
> > > kernel is incredibly improving (against my expectations).
> > >
> > > http://www.osadl.org/Single-View.111+M5b96e97f67b.0.html
> > >
> > > I'd like to know if the implementation of OSD-library is implemented
>
> in
>
> > > such a manner that the kernel-level threads can reflect the priority
> > > given by the user to the scheduling of epicsThreads?
> > >
> > > In other words, can I benefit from the improvement of Linux kernel
> > > without making any changes in EPICS source codes?
> >
> > in file base/configure/CONFIG_SITE
> >
> > change
> >
> > USE_POSIX_THREAD_PRIORITY_SCHEDULING = NO
> >
> > to
> >
> > USE_POSIX_THREAD_PRIORITY_SCHEDULING = YES
> >
> > Also you must start the IOC as root.
> >
> > Marty



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