Re: [Xenomai-core] XENO_OPT_SYS_STACKPOOLSZ vs. switchtest

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

Philippe Gerum 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.
> 
> Nope. An individual 4k request is going to pull 8 x 512 bytes pages from the
> stack pool, not more.

Yeah, I see. The only "overhead" here was already paid via the pagemap.

> 
>  Reminds me of TLSF - if I only had the time... :)
> 
> It looks like working properly for -solo.

I think to remember your concerns were more about missing fragmentation,
size overhead and performance comparisons. A working version for
standard Xenomai was already available at that time (maybe not for all
archs, but that is surely quickly fixed).

Jan

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