memory overhead of rtems regions

[Gedare Bloom]

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
>> >