Re: [Xenomai-help] native: A 32k stack is not always a 'reasonable' size

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Peter Soetens wrote:
> On Wed, Jul 7, 2010 at 11:06 AM, Gilles Chanteperdrix
> <gilles.chanteperdrix@xenomai.org> wrote:
>> Peter Soetens wrote:
>>> At least, not for Orocos applications. We've had hard to debug
>>> application segfaults that used just a 'little' bit more than 32k. We
>>> had to raise the stack size to 128k to get reliably through our
>>> application startup. I stem from the old 'mlockall ate my RAM'
>>> generation where we typically reduced stack sizes in order to have
>>> some crumbles left for the heap. But 32k wasn't really what we were
>>> aiming for.
>>>
>>> Maybe we should explicitly document the 32k limit and its limitations
>>> for certain applications...?
>> Again, things have been fixed in 2.5.3 with regard to stack sizes, could
>> you check that you have the same behaviour?
> 
> I think we had, but I'm uncertain right now.
> 
>> As for 32KiB, it is only a default stack size, it is only reasonable in
>> the sense that 2MiB is unreasonable on a low-end system. 32KiB was
>> picked because it allows printf to work. Now, whatever stack size we
>> choose, there will be applications which need more, this does not really
>> make the default unreasonable.
> 
> I knew you would say that. It deserves an entry in the faq or some
> trouble shooting document though.

It is documented. For instance, rt_task_create says:
stksize 	The size of the stack (in bytes) for the new task. If
		zero is passed, a reasonable pre-defined size will be substituted.

What else can we say? Documenting that this size is 32 KiB would be
wrong, because we do not want applications to rely on a particular
value, in case we want to change it. And the fact that if your stack is
too small, you will get problems is kind of obvious. For anyone having
played with stack sizes with Linux or any proprietary RTOS, at least.

-- 
					    Gilles.