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SubjectRe: PREEMPT_RT vs ADEOS: the numbers, part 1

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

> Ingo Molnar wrote:
> > 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?
>
> This is all done in kernelspace. I'll check with Kristian for the
> rest. In the mean time, let me know if you have any recommendations
> based on the fact that it's indeed in the kernel.

if you want to measure hw-interrupt delays then under PREEMPT_RT you'll
need to use an SA_NODELAY interrupt handler. (which is a PREEMPT_RT
specific flag) If you use normal request_irq() or some parport driver
then the driver function will run in an interrupt thread and what you
are measuring is not interrupt latency but rescheduling latency.

Ingo
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