memory overhead of rtems regions

[Gedare Bloom]

Matthew,

Is there an easy way to find this optimal size? If so maybe you could
post it or better yet document it in the region documentation :)

On Thu, Mar 7, 2013 at 11:44 AM, Matthew J Fletcher <amimjf at gmail.com> wrote:
> Gedare,
>
> Thanks for the advice, for this particular region that's the optimal size,
> I've done a bit of experimentation and you can find an optimal size for most
> allocations.
>
> On 7 Mar 2013 14:38, "Gedare Bloom" <gedare at rtems.org> wrote:
>>
>> Looking closer, your allocations are multiples of 40. You should set
>> the page_size to 40 in your region create.
>>
>> On Thu, Mar 7, 2013 at 9:37 AM, Gedare Bloom <gedare at rtems.org> wrote:
>> > You're right. The error return does indicate that memory ran out. It's
>> > not clear if the memory that ran out is heap or workspace.
>> >
>> > You set a page_size of 128, and then make allocations in multiples of
>> > 10. I think the segments that get returned are allocated as multiples
>> > of the page_size. So there will be some fragmentation issues. E.g. a
>> > request for a segment of size 400 will return a 512 size segment,
>> > wasting 112 bytes. This is stated in the C User Manual section about
>> > Regions [1]. This fragmentation is probably causing the problem.
>> >
>> > -Gedare
>> >
>> > [1]
>> > http://rtems.org/onlinedocs/doc-current/share/rtems/html/c_user/Region-Manager-Region-Manager-Definitions.html#Region-Manager-Region-Manager-Definitions
>> >
>> > On Thu, Mar 7, 2013 at 9:21 AM, Matthew J Fletcher <amimjf at gmail.com>
>> > wrote:
>> >> Hi,
>> >>
>> >> Its 20, but I believe that would return RTEMS_TO_MANY, if that was not
>> >> enough.
>> >>
>> >> On 7 Mar 2013 14:09, "Gedare Bloom" <gedare at rtems.org> wrote:
>> >>>
>> >>> Check how many message queues your application has configured.
>> >>>
>> >>> #define CONFIGURE_MAXIMUM_MESSAGE_QUEUES    ?
>> >>>
>> >>> On Thu, Mar 7, 2013 at 7:05 AM, Matthew J Fletcher <amimjf at gmail.com>
>> >>> wrote:
>> >>> > Hi,
>> >>> >
>> >>> > Reading the documentation for rtems regions is a bit vague about the
>> >>> > overhead of the lists that behind the scenes manage the blocks. Its
>> >>> > quite
>> >>> > possible i am not fully understanding the operation. I have a call
>> >>> > sequence
>> >>> > as follows.
>> >>> >
>> >>> > rtems_region_create( length = 19800, page_size = 128 )
>> >>> >   rtems_region_get_segment( size = 160 )
>> >>> >     rtems_message_queue_create ( count = 160, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 400 )
>> >>> >     rtems_message_queue_create ( count = 400, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 1600 )
>> >>> >     rtems_message_queue_create ( count = 1600, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 40 )
>> >>> >     rtems_message_queue_create ( count = 40, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 4000 )
>> >>> >     rtems_message_queue_create ( count = 4000, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 40 )
>> >>> >     rtems_message_queue_create ( count = 40, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 40 )
>> >>> >     rtems_message_queue_create ( count = 40, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 40 )
>> >>> >     rtems_message_queue_create ( count = 40, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 40 )
>> >>> >     rtems_message_queue_create ( count = 40, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 120 )
>> >>> >     rtems_message_queue_create ( count = 120, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 400 )
>> >>> >     rtems_message_queue_create ( count = 400, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 400 )
>> >>> >     rtems_message_queue_create ( count = 400, max_size =2 )
>> >>> >   rtems_region_get_segment( size = 2000 ) // total size upto here
>> >>> > 7320
>> >>> >     rtems_message_queue_create ( count = 2000, max_size =2 )
>> >>> >     // returns RTEMS_UNSATISFIED - unable to allocate message
>> >>> > buffers
>> >>> > here
>> >>> >
>> >>> > I dont fully understand why RTEMS_UNSATISFIED is being returned from
>> >>> > the
>> >>> > queue_create(), is there really a 50%+ overhead in managing 128 byte
>> >>> > pages ?
>> >>> > out of a 19800 length.
>> >>> >
>> >>> > I am presuming that the RTEMS_UNSATISFIED is because of the region
>> >>> > size,
>> >>> > but
>> >>> > i could be wrong about that.
>> >>> >
>> >>> >
>> >>> > regards
>> >>> > ---
>> >>> > Matthew J Fletcher
>> >>> >
>> >>> >
>> >>> > _______________________________________________
>> >>> > rtems-users mailing list
>> >>> > rtems-users at rtems.org
>> >>> > http://www.rtems.org/mailman/listinfo/rtems-users
>> >>> >