Re: [Xenomai-core] XENO_OPT_SYS_STACKPOOLSZ vs. switchtest

[Philippe Gerum <rpm@xenomai.org>]

Jan Kiszka wrote:
> 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).
>

Locking and init fixes went to TLSF 2.4.4 in the recent months, so we would have
needed those anyway. It's quite late to merge TLSF in Xenomai 2.5, but I would
have no objection to make it the base allocator of the 3.x series. We would have
to extend it with:

- support for a few callouts, such as the validity checking function used in
xnhead_test_and_free(),
- shared memory export (this is quite allocator agnostic in fact)
- detailed error codes in xnheap_test_and_free/xnheap_free

> Jan
> 


-- 
Philippe.