On Tue, 2006-02-21 at 20:49 -0500, Lee Revell wrote:
> On Tue, 2006-02-21 at 19:30 -0600, Jan Depner wrote:
> > On Tue, 2006-02-21 at 15:28 -0500, Lee Revell wrote:
> > > On Tue, 2006-02-21 at 13:19 -0600, Jan Depner wrote:
> > > > There's a bunch of information on that on my site (albeit outdated).
> > > > Tuning the disk drives is a must and it *will* help but there are
> > > > instances where the disk drive is busy and you can't get to it no
> > > > matter
> > > > how well tuned it is. I prefer to minimize any chance of that. You
> > > > have to remember that unless you're running RTLinux or VXWorks (or DOS
> > > > or VMS) you're not running a hard real time system. Shit happens.
> > > >
> > >
> > > The -rt kernel with fuill preemption actually is a hard real time system
> > > (no one claims it is in the same league of reliability as QNX or
> > > VXWorks, yet...) - it should be able to guarantee response times.
> > >
> >
> > While I agree that it's very good it's not hard real-time. It can't
> > do guaranteed 15 microsecond interrupt response. It is a very good soft
> > real-time system.
> >
>
> Hard RT is not about what the response time is, it's about whether you
> can guarantee to make some arbitrary deadline, which the -rt patch can
> theoretically do (I say theoretically because you still would have to
> audit a limited set of code paths for RT safeness).
>
I beg to differ. Hard real-time guarantees the response time. Most
good hard real-time systems actually do respond in the 10-15 microsecond
range (though that is not a requirement of hard real-time). Theory has
no place in hard real-time. Check with Monta Vista and see if they
think the kernel with RT patches is hard real-time.
--
Jan 'Evil Twin' Depner
The Fuzzy Dice
http://myweb.cableone.net/eviltwin69/fuzzy.html
"As we enjoy great advantages from the invention of others, we should be
glad of an opportunity to serve others by any invention of ours, and
this we should do freely and generously."
Benjamin Franklin, on declining patents offered by the governor of
Pennsylvania for his "Pennsylvania Fireplace", c. 1744
