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Date: Tue, 19 Jun 2012 11:29:57 +0200
From: Wolfgang Grandegger <wg@grandegger.com>
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Subject: Re: [Xenomai] Sharing memory between rt-posix and standard-posix
 apps
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: Xenomai@xenomai.org

On 06/19/2012 11:04 AM, Gilles Chanteperdrix wrote:
> On 06/19/2012 10:52 AM, Wolfgang Grandegger wrote:
>> On 06/19/2012 10:50 AM, Gilles Chanteperdrix wrote:
>>> On 06/19/2012 10:49 AM, Wolfgang Grandegger wrote:
>>>> On 06/19/2012 10:33 AM, Gilles Chanteperdrix wrote:
>>>>> On 06/19/2012 10:25 AM, Wolfgang Grandegger wrote:
>>>>>> Hello,
>>>>>>
>>>>>> the shared memory support of Xenomai's POSIX skin currently only support
>>>>>> shared memory between rt processes.
>>>>>
>>>>> These services are for sharing memory between user-space and
>>>>> kernel-space. In order to share memory between user-space processes, you
>>>>> can use plain linux shared memories.
>>>>
>>>> But then I will get mode switches due to page faults, right?
>>>
>>> No, there should not be any page fault.
>>
>> But that's what we observe on a i.MX53 and i.MX6Q board. IIRC, the first
>> access usually results in a page fault.
> 
> And you do not get the same behaviour with posix skin shared memories ?

Right, and that's because do_pagefault() is called somewhere in the
initialization, IIRC. But I will redo my tests now.

Anyway, if I use the POSIX skin the shared memory functions in there
will be used automatically. But I could use  __real_shm_open and
__real_mmap, right? ... and access the page once per page in the
initialization phase. Then no more page faults should happen.

Wolfgang.