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Date: Thu, 03 Dec 2009 14:14:25 +0100
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai-core] Realtime gettimeofday()
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To: Wolfgang Mauerer <wm@domain.hid>
Cc: Jan Kiszka <jan.kiszka@domain.hid>, "xenomai@xenomai.org" <xenomai@xenomai.org>

Wolfgang Mauerer wrote:
> Hi,
> 
> Gilles Chanteperdrix wrote:
>> Wolfgang Mauerer wrote:
> 
>>> So that means, in essence, that you would accept probabilistic  
>>> algorithms in realtime context?
>> Ah, today's troll!
> 
> though it seems that I have to replace Jan this time ;-)
>> As I think I explained, the use of a seqlock in real-time context when
>> the seqlock writer only happens in linux context is not probabilistic.
>> It will work every time the first pass.
> 
> I still don't see why it should succeed every time: What about
> the case that the Linux kernel on CPU0 updates the data, while
> Xenomai accesses them on another CPU? This can lead to
> inconsistent data, and they must be reread on the Xenomai side.

Yeah, right. I was not thinking about SMP. But admit that in this case,
there will be only one retry, there is nothing pathological.

> 
> I'm asking because if this case can not happen, then there's
> nothing left to to as I have the code already at hand.

You have reworked the nucleus timers handling to adapt to this new
real-time clock ?

-- 
                                          Gilles