Re: [Xenomai] minimum xenomai stack size (mercury)

[Philippe Gerum <rpm@xenomai.org>]

On 08/19/2015 01:03 PM, Thomas De Schampheleire wrote:
> On Fri, Jul 24, 2015 at 2:48 PM, Thomas De Schampheleire
> <patrickdepinguin+xenomai@gmail.com> wrote:
>> Hi,
>>
>> With Xenomai Mercury (specifically the PSOS skin, but that doesn't
>> matter for this question), the minimal stack size applied is
>> PTHREAD_STACK_MIN * 4, even if the caller requested a smaller one.
>>
>> On MIPS, and some other architectures, PTHREAD_STACK_MIN is already 128K:
>> (<glibc>/ports/sysdeps/unix/sysv/linux/mips/nptl/bits/local_lim.h)
>>
>> /* Minimum size for a thread. At least two pages with 64k pages. */
>> #define PTHREAD_STACK_MIN 131072
>>
>> With Xenomai multiplying this with 4, every thread has half a megabyte
>> of stack, which is way too much for systems with a large number of
>> threads.
>> It is possible to limit this in other ways, by setting 'ulimit -s 128'
>> for example, but it is a dirty workaround in my opinion.
>>
>> What is the real minimum stack requirement for Xenomai? I cannot
>> imagine that this is in the order of 512K.
>>
>> With PTHREAD_STACK_MIN varying so much on different platforms, what
>> about code like:
>>
>> minimum_stacksize = MAX(XENOMAI_STACK_MIN, PTHREAD_STACK_MIN);
>>
>> if (stacksize < minimum_stacksize) {
>>     stacksize = minimum_stacksize;
>> }
>>
>> where XENOMAI_STACK_MIN is a value that is not calculated based on
>> PTHREAD_STACK_MIN?
>>
>> With this approach, systems with 16K PTHREAD_STACK_MIN could still get
>> 64K minimum stack in case the xenomai minimum stack size is 64K, while
>> not negatively impacting systems that have 128K PTHREAD_STACK_MIN.
>>
>> (Note that for systems with 4K/8K pages, the PTHREAD_STACK_MIN of 128K
>> (two 'pages' taken for 64K) is already very exaggerated)
>>
> 
> Ping?
> 

Since there is no reliable way to define XENOMAI_STACK_MIN, the most
flexible approach would be to use PTHREAD_STACK_MIN as the default value
(instead of x 4), expecting the code creating threads to specify the
stack size they need (e.g. the ustack parameter to t_create() with the
pSOS emulator).

-- 
Philippe.