Re: [Xenomai-help] gpioirqbench: measuring external interrupt latencies

[Jan Kiszka <jan.kiszka@domain.hid>]

[-- Attachment #1: Type: text/plain, Size: 2853 bytes --]

Wolfgang Grandegger wrote:
> Jan Kiszka wrote:
>> Wolfgang Grandegger wrote:
>>> Hello,
>>>
>>> I'm proud to announce "gpioirqbench", a benchmark tool to measure
>>> external interrupt latencies. It is derived from Jan's irqbench [1] for
>>> the PC. Instead of using the serial or parallel port, it uses GPIO pins
>>> on embedded systems. It measures the time between the generation of an
>>> interrupt triggered by a GPIO pin and the reply by either the interrupt
>>> service routine, a kernel-space task or a user-space task. As reply,
>>> another GPIO pin will be toggled. The setup consists of two systems, the
>>> log host and the test target. The log host triggers the interrupt on the
>>> test target and measures the latency. This benchmark is primarily for
>>> Xenomai/RTDM, but it can also be used for plain Linux or even Linux-rt
>>> (with the real-time preemption patch).
>> Nice stuff! Still I have a few conceptual questions: :->
> 
> I did expect them ;-).
> 
>> 1. Why do you need a Xenomai measurement host? On first glance, you are
>>    just spinning on the reply for the RT target. Why not use plain Linux
>>    for this to increase portability? Most beautiful would be a pure
>>    userspace approach like for irqbench. What prevents this here?
> 
> Well, I'm not a hardware expert and therefore it was not obvious to me
> how to connect GPIO pins to the standard PC. To avoid electrical
> incompatibilities, I chose my good old TQM855L module as log host.
> I agree, that this solution is rather special and that the one for
> irqbench would be much better. Any ideas how to interface GPIO pins with
> the PC?

Misunderstanding: I'm not talking about porting the host part to a PC, 
that is a different thing and surely involves some hardware work (unless 
the PC board already has compatible IO ports). I was talking about 
running the host part on _plain_ Linux on whatever arch providing the IO 
hardware, and maybe also running it without a kernel helper (by poking 
directly into to IO - if that is feasible). Latency-wise there is no 
need for a RTOS on the host side as you run the critical part with IRQs 
disabled.

> 
>> 2. Do you see a chance to integrate the target'S GPIO interface into the
>>    exiting irqbench backend? That would make it easy to merge the
>>    Xenomai version into the tree.
> 
> In the end I preferred to make a separated distribution, as various
> parts are very hardware specific and the driver can also be built as
> normal Linux character device driver.

I don't want to replace your distribution, I want to enhance the Xenomai 
benchmark that comes with the releases. And maybe I also want to trigger 
the development of more standard benchmark tools (compatible kernel/user 
APIs on the targets, reusable host-side tools). :)

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 250 bytes --]