Messages in this thread | | | From | yodaiken@chelm ... | Subject | Re: real-time support in Linux (again) | Date | Sun, 28 Feb 1999 19:15:06 -7900 (MST) |
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> > yodaiken@chelm.cs.nmt.edu writes: > > > what's the difference between using rtlinux for real-time and linux for > > > time-sharing, and Sun's approach with Solaris where the scheduler > > > algorithms are contained in something akin to loadable kernel modules? > > > > Sun advertises 2millisecond worst case response time on a dual > > processor that is only running their "rt" on one processor. RTlinux > > gives 40microsecond response time on a single 486. So the difference > > is about 2 orders of magnitude in performance and plus 3 more in > > cost. > > >From when is that response time measured? From the time the CPU enters > the interrupt handler, or from the time the interrupt hits the CPU?
I'm sorry, but I mistated things. The 40microseconds is worst case jitter on a periodic task that measures jitter by reading the timer and looking at the difference between expected and actual time. On a P5 or better we use the rdtsc and get a lower number -- low 30s. Interrupt latency is significantly better then that, because some of this jitter is caused by the timer itself. I haven't measured this recently, but according to some people who have on the RTL list, the times are somewhere under 10us on a decent PII. All of this is time from asserting the interrupt to handler response. The time from entry of handler seems meaningless.
> > Also, the 2 ms case Sun quotes: what kind of hardware is that?
I saw that for a dual ultrasparc. >
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