Re: [Xenomai-core] XENO_OPT_SYS_STACKPOOLSZ vs. switchtest

[Jan Kiszka <jan.kiszka@domain.hid>]

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... :)

Jan

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