Stephen D. Cohen wrote:
> > The above is totally wrong as when you get to the thread managing the
> > interrupt you need the FPUsave/restore anyhow, and so end up
> > in loosing
> > efficiency as you pay for the thread switch overhead.
>
> But get out of an ISR quickly. Why sit in an ISR and pre-empt the
> regular scheduling when it is not necessary? Some ISRs would, conceptually,
> be lower priority than other tasks. By getting out of the ISR as quickly as
> possible, it gives the regular priority mechanisms the opportunity to do the
> "right thing" for the system. It also gives lower priority interrupts a
> crack at the CPU when necessary.
>
> > Once more if you need to use the FPU sooner or later you have to save
> > restore it and adding a task switch to keep it "elegant" is
> > just adding
> > overhead.
>
> To regain the function of the scheduler and priority structure of
> the RTOS.
Clearly you missed what I stated in other mails:
- doing it in ISR is usefull if that is the only real time task. I now
add: or if what you are doing will go in the highest priority task
anyhow;
- on MPs you must be carefull to have the interrupt on the CPU running
your real time task, otherwise you need to message another CPU, with a
lot more jitter;
- the fact that RTAI has always had such a capability proves that here
we do not take it for granted and are happy to make anybody at ease with
what he/she likes to do. BTW: now vanilla Linux 2.3(4).whatever has such
a capability and also RTL V3 can do it.
- allowing the lower priority inturrupts is just a matter of enabling
interrupts and acknowledging the PIC approriately.
That said anybody can do what he/she wants and the result can be just
the same. You have only to avoid conveying the idea that FP cannot be
used in kernel space. It is simply not true. What is true is that some
people do not like it that way.
Ciao, Paolo.
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