Markus Franke wrote:
> Dear all,
> 
> I am running some latency tests with irqbench/irqloop. I am wondering
> whether it would be possible to achieve better results when activating
> CONFIG_PREEMPT and CONFIG_PREEMPT_VOLUNTARILY during the kernel
> configuration and running irqloop in User Mode over this kernel?

Nope.

> Does it make any sense?

Nope. :)

> I think in theory it should give better results because
> this irqloop runs in secondary(linux) domain when started, right? An
> increasing preemptibility of the linux kernel should be better for the
> irqloop-task.

The Linux kernel is already fully preemptible by Xenomai once you
applied the I-pipe patch. Therefore, you are free to pick the Linux
preemption strategy according to your *Linux* load, independent of what
the real-time part needs.

Unless you have interactive Linux programs running, I can suggest to
pick PREEMPT_VOLUNTARILY or even PREEMPT_NONE, specifically on low-end
hardware.

> All tests were made under heavy I/O and CPU load by means of "dd",
> "pingflood" and "cpuburn". Nevertheless, I can only achieve worse
> results when activating CONFIG_PREEMPT.

Do you have CONFIG_DEBUG_PREEMPT set as well then? This option still as
a small but measurable impact on Xenomai due to micro-dependencies that
as scheduled to be removed in the near future.

Jan