Re: [Xenomai] Some Information About compilation Xenomai and RT Patches

[Philippe Gerum <rpm@xenomai.org>]

On 06/17/2014 05:00 PM, Jean Rodriguez wrote:
> Hi guys,
>
> I’m trying to compile kernel 3.8 with the last xenomai source.
>
> I want to know some precisions about preempt option.
>
> Is it useless to patch the kernel with with Xenomai and also with RT patch
> from kernel.org?

Combining both makes sense only if your use case involves response time 
requirements when running regular linux activities, in addition to the 
real-time duties offloaded to the Xenomai co-kernel. In most cases where 
a dual kernel solution applies, there is no requirement for full 
preemption (-rt) on the regular linux side though.

>
> Because With RT patch I can choose on menuconfig  Preemption Model 5 choices
> (No preempt, Voluntary and low latency , preemptible kernel or fully
> preemptivekernel)
>
> But if I patch only with xenomai I have just 3 choices of preemptive (No
> preempt, Voluntary and low latency)
>

Those choices affect the regular linux kernel behavior only, not 
Xenomai. When the Xenomai co-kernel is present, there is no need for 
additional preemption models, the linux kernel is inherently preemptible 
by Xenomai activities at any time.

> If patch first with RT and after xenomai I have a lot of Hunk message
> (warning and error) but if  I Patch first with xenomai and after RT -> no
> problem
>
>
>
> So my question are they compatible together? Or perhaps choosing fully
> preemptive will turn my system unstable.
>

Combining both is possible, and such configuration is actually used by 
some projects. However, a combo patch merging preempt-rt and the I-pipe 
has to be specifically crafted for the target kernel.

>
>
> My goal is to catch Interruption with a small latency (50-10 µs) with a low
> processor charge

Since there is no one-fits-it-all solution, I would suggest to benchmark 
each configuration separately for your use case, and see which one best 
fits the bill, taking into account the pros and cons of each approach in 
the long run for your project.

>
> Board  Arbor card
> <http://www.arbor.com.tw/product/product.aspx?Product_Name=EmETX-i2900&os_id
> =1&version=+Default> EmETX-i2900  with ATOM N450
>
>
>
>
>
> Thanks for your future response
>
>
>
>
>
> Kind regards,
>
>
>
> Jean Rodriguez
>
> Ingénieur R&D Informatique
>
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> ---
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-- 
Philippe.