Maryam Moghaddas wrote:
>
> >
> >
> > Both RTLinux (beta16) and RTAI (version 0.6) are very stable, and both
> > have support for pthreads.
> > The main differences in the pthreads support that I'm aware of are:
> >
> > - RTAI has support for conditional variables and priority inheritance
> > mutexes whereas RTLinux does not.
> >
> > - RTAI has support for dynamic thread creation, whereas in RTLinux all
> > the threads must be created at init_module time.
> >
>
> Thanx for your great reply,
> One thing I am not clear of is I am currently using RTLINUX V1. What is the
>difference
> if I use Linux pthreads on the RTlinuxV1 environment, instead of using your
>suggestions?
> difference interms of realtime performance...
> Best regards,
> m
The Linux threads package is completely separate to RTLinux, and
operates on standard Linux systems with or without RTLinux.
If you use the Linux pthreads package then the threads are created as
user space processes which can access each others memory.
You can lock the threads into memory which will prevent them from being
swapped out, and also give them a scheduling policy of SCHED_FIFO or
SCHED_RR which gives them higher priority than ordinary Linux processes.
However the threads can still be locked out by Linux kernel activity.
What this means is that on lightly loaded systems good realtime
performance can be obtained using Linux threads, however if the system
loading increases, particularly disk activity, then the threads will be
locked out by kernel activity for significant periods of time. The
actual periods of lock out will be very dependent on the the system
configuration etc etc, but times in excess of 60 mS are not unusual.
So I guess it depends on your application, if it requires guaranteed
deadlines and/or latencies then it is unlikely that Linux threads will
meet the specifications and one of the RT variants should be used, but
if your application can withstand missing the occasional deadline, or
possibly have exclusive use of the system, then Linux threads may well
be acceptable.
Best regards,
Steve
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