Re: PREEMPT_RT vs ADEOS: the numbers, part 1

Ingo Molnar
2005-06-12T06:35:55Z

* Karim Yaghmour <karim@opersys.com> wrote:

> Ingo Molnar wrote:
> > how were interrupt response times measured, precisely? What did the
> > target (measured) system have to do to respond to an interrupt? Did you
> > use the RTC to measure IRQ latencies?
>
> The logger used two TSC values. One prior to shooting the interrupt to
> the target, and one when receiving the response. Responding to an
> interrupt meant that a driver was hooked to the target's parallel port
> interrupt and simply acted by toggling an output pin on the parallel
> port, which in turn was hooked onto the logger's parallel port in a
> similar fashion. We'll post the code for all components (both logger
> and target) for everyone to review. There's no validity in any tests
> if others can't analyze/criticize/ duplicate.

ok, this method should work fine. I suspect you increased the parport
IRQ's priority to the maximum on the PREEMPT_RT kernel, correct? Was
there any userspace thread on the target system (receiving the parport
request and sending the reply), or was it all done in a kernelspace
parport driver?

Ingo