On Wed, Mar 22, 2000 at 06:02:24PM +0100, David Olofson wrote:
> Wed, 22 Mar 2000 [EMAIL PROTECTED] wrote:
> > (BTW: from the Linux man page:
> > As SCHED_FIFO and SCHED_RR processes can preempt
> > other processes forever, only root processes are allowed to activate these
> > policies under Linux.
> > )
>
> Yep, you have to have *some* kind of adrenaline rush left with protected memory
> and all! ;-) If you want to be completely safe, you could always throw in a
> watchdog thread or something... I was thinking Magic SysRq key to kill the
> current (SCHED_FIFO or SCHED_RR) thread as another alternative, but I might be
> missing something that already exists.
There are many peculiar problems coming from running "RT" in a Linux environment:
this is why the RTLinux design puts the RT threads outside of Linux. Look
at the curent Linux scheduler to see how un-simple coping with SCHED_RR gets.
I'm thinking of adding RT schedulable Linux processes that run solely in user
space -- when they do a syscall they fall out of RT scheduling.
They would be memory protected and able to access standard libraries: they
would really only be useful for high precision compute tasks and should connect
to RT via fifos. Is there much interest in such a feature?
> And as for the root privileges requirement, it has been discussed adding a
> "real time" user group capability instead. (I'm not up to date with this,
> though.) Running RT apps as root just for the scheduling is not all that nice in
> production systems, especially not if they are going to run user installed
> third-party plugins in those threads...
On Linux, I think if you are going to run SCHED_RR you better either be root
or be created by a root privelege "scheduler". SCHED_RR is too dangerous.
--
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Victor Yodaiken
FSMLabs: www.fsmlabs.com www.rtlinux.com
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