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SubjectRe: real-time support in Linux (again)
yodaiken@chelm.cs.nmt.edu writes:
> >
> > 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.

OK. BTW: I don't see where/what the 3 orders of magnitude cost
difference comes from. I just see 2 orders of magnitude.

> The time from entry of handler seems meaningless.

Not to marketdroids.

> > Also, the 2 ms case Sun quotes: what kind of hardware is that?
>
> I saw that for a dual ultrasparc.

<smirk>

Regards,

Richard....

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