test for rtems_workspace_greedy_allocate

[Sebastian Huber]

On 09/02/2021 23:17, Chris Johns wrote:

> On 10/2/21 1:10 am, Sebastian Huber wrote:
>> On 09/02/2021 14:59, Gedare Bloom wrote:
>>
>>>> sbrk() cannot be removed and we need to maintained and test it as a BSP level
>>>> interface.
>>>>
>>>> This is an nice design idea where the sbrk() pool of memory can be given out to
>>>> the heap or workspace depending on the demands of the application. I can see
>>>> this being important to application frameworks like EPICS and so something we
>>>> should look to add to all architectures.
>>>>
>>>    Please raise a ticket, this can be a GSoC project idea I think?
>> What is the benefit of sbrk() compared to the unified work areas? Do address
>> fragmentation/performance issues it makes more sense to replace the first fit
>> allocator with something else.
> Good question. A couple of points come to mind ...

With unified work areas I mean this configuration option:

https://docs.rtems.org/branches/master/c-user/config/general.html#configure-unified-work-areas

>
> A unified workspace has the workspace and heap at different ends of the memory
> gowing towards each other while sbrk has the blocks in closer proximity and
> interleaved. Would there be performance differences with caches and SMP? For
> example creating tasks each with some dynamic memory.
For a real SMP system (note: symmetric), it doesn't matter at which 
physical address range your allocated memory is. However, the lager SMP 
systems are really NUMA systems with different memory controllers and 
some sort of on-chip network. For this you need a domain based memory 
allocator. FreeBSD has such an allocator: UMA.
>
> The unified address space requires memory be continuous and sbrk() does not.

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