[Xenomai-help] Xenomai and select() function - don't work correctly

[Xenomai-help] Xenomai and select() function - don't work correctly

[Jens Köhler]

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Hello,

on my atom processor based computer is Xenomai installed. (Kernel 2.6.26,
1000Hz, Xenomai 2.4.10, PREEMPT patch, no xenomai application running).

A normal linux application reads serial data from an UART
(16550A) and checks by select() function if there are new received
bytes. Select() has a timeout parameter, set to 12 milliseconds. Some times
it happens that select() waits 43 ms instead of maximum 12 ms. Result value
of select() is timeout instead of "byte received". Could this caused by
Xenomai? How could I improve it?

Thanks and regards,
Jens

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Re: [Xenomai-help] Xenomai and select() function - don't work correctly

[Gilles Chanteperdrix]

Jens Köhler wrote:
> Hello,
> 
> on my atom processor based computer is Xenomai installed. (Kernel 2.6.26,
> 1000Hz, Xenomai 2.4.10, PREEMPT patch, no xenomai application running).
> 
> A normal linux application reads serial data from an UART
> (16550A) and checks by select() function if there are new received
> bytes. Select() has a timeout parameter, set to 12 milliseconds. Some times
> it happens that select() waits 43 ms instead of maximum 12 ms. Result value
> of select() is timeout instead of "byte received". Could this caused by
> Xenomai?

Run the same test without enabling Xenomai in the kernel configuration,
and you will know.

> How could I improve it?

Well basically, you are complaining that Linux is not real-time. We know
that, this is the reason why real-time extensions such as Xenomai or
preempt_rt exist.

-- 
                                                                Gilles.

Re: [Xenomai-help] Xenomai and select() function - don't work correctly

[Jan Kiszka]

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On 2011-03-18 12:48, Jens Köhler wrote:
> Hello,
> 
> on my atom processor based computer is Xenomai installed. (Kernel 2.6.26,
> 1000Hz, Xenomai 2.4.10, PREEMPT patch, no xenomai application running).

What does "PREEMPT patch" mean? CONFIG_PREEMPT? Then try over a recent
kernel (2.6.37) with latest ipipe patch as we fixed several issues that
affected Linux task preemption negatively on x86-32.

Jan


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Re: [Xenomai-help] Xenomai and select() function - don't work correctly

[Jens Köhler]

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Yes, CONFIG_PREEMPT is set. We will try in first step what happens when it's
not set.

Thanks,
Jens

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Re: [Xenomai-help] Xenomai and select() function - don't work correctly

[Gilles Chanteperdrix]

Jens Köhler wrote:
> Yes, CONFIG_PREEMPT is set. We will try in first step what happens when it's
> not set.

I am sorry to insist, but IMO, you should try disabling CONFIG_XENOMAI
and CONFIG_IPIPE in the kernel configuration, in order to be sure that
these options are causing what you are seeing.

-- 
                                                                Gilles.