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Date: Thu, 19 Feb 2009 16:46:14 +0100
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-core] XENO_OPT_SYS_STACKPOOLSZ vs. switchtest
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: xenomai-core <xenomai@xenomai.org>

Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Philippe Gerum wrote:
>>> Jan Kiszka wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> Jan Kiszka wrote:
>>>>>> Gilles Chanteperdrix wrote:
>>>>>>> Jan Kiszka wrote:
>>>>>>>> Hi Gilles,
>>>>>>>>
>>>>>>>> how much XENO_OPT_SYS_STACKPOOLSZ do I need to run switchtest for
>>>>>>>> default settings? At least on x86-64, the default 32K is not enough.
>>>>>>>> Unless we talk about GB ;), maybe it makes sense to adjust the default
>>>>>>>> size accordingly.
>>>>>>> It depends on the arguments you pass to switchtest.
>>>>>> None, ie. the default settings.
>>>>> Then 6 kernel-space tasks are created. Since switchtest is not the
>>>> 6*4 is 20k... Ah, the well-known allocator overhead, I guess. Will try
>>>> with >= 40k.
>>>>
>>> Actually, it is not really an overhead, but rather the fact that it wants at
>>> least two initially free pages per heap.
>> That would make 22K. The problem is that the management overhead is
>> rounded up to another full page, requiring a 8K allocation per 4K
>> request. Reminds me of TLSF - if I only had the time... :)
> 
> When allocating 4K, only 4K are allocated.
> 
> I think the problem could rather be that you are running switchtest on a
> multi-cpu system, in which same the number of cpu tasks created is 6 by cpu.

That was in fact the problem here. OK, so we should just consider
adjusting the pool default for 8K-stack archs (PowerPC64, Blackfin, and
maybe also x86-64).

Jan

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