Solaris 10 real-time support on a uniprocessor system

Question

Hello,
I've read older documentation stating that Solaris has real-time support on a dual processor system. One of the CPUs is dedicated to the real time tasks. I was wondering
if this is an absolute requirement. Could one use Solaris 10 as a real-time OS on a uni-processor system?
Thanks for your help.
Stephen

Answer 1

Stephen,
Solaris is capable of running processes in real-time mode on either a uni- or multiprocessor machine. real-time mode is implemented at the scheduler level, with RT class processes layered on top of TS/IA and SYS processes. This is mostly implemented through priority levels (0-59 for TS/IA, 60-99 for SYS, 100-159 for RT [if used]). For details regarding this, pls. see priocntl(1).
Be aware of a couple of gotchas, though:
- RT processes will stay at their priority level, no matter what.
- They will not be subject to time-sliced scheduling (in fact, they won't be scheduled in normal ways, since the scheduler itself runs at SYS priority level!)
- They'll not stop running until they either voluntarily give up the CPU by means of something like swtch(), or block on a resource, or any process with an even higher priority becomes runnable.
In short, they might render your system more or less inoperable, if used without caution.
Consider it a BAD idea to put your shell into RT mode - and definitely do NOT try to run largely computational tasks (PI to the nth position, as an example) in RT mode, just to get some more performance out of your box! It won't work as you expect it.
RT is meant to run fairly short routines that require (almost ) deterministic response - such as acting on a signal from a sensor on an assembly line. It's definitely not a way to obtain better response times or outperform your peers.
Solaris, as any UNIX, is not an outright RT system - it just has some stuff built into it that could help in running it as if it were one.
Consider well what you're about to do, then reconsider ... ;) Don't say you haven't been warned.
HIH, kind regards,
- Tom