Re: [Xenomai-help] mq_send takes longer than expected

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Gilles Chanteperdrix wrote:
> Gilles Chanteperdrix wrote:
>> Steve wrote:
>>> Hi,
>>>
>>> Calling mq_send takes significantly varied amounts of time depending
>>> on the queue length.  I was not expecting this behaviour, particularly
>>> as this does not happen when using RTAI mq_send calls.  I can
>>> understand that queue creation / opening times will heavily depend on
>>> the queue's overall size, however I would have thought that sending a
>>> message (adding it to the queue's data structure (linked list?)) would
>>> take a constant time.
>>>
>>> Is this a bug, or expected behaviour?  I have attached an example.
>> mq_send is expected by the posix specification to block its caller when
>> the queue is full. If you do not want this behaviour, you should pass
>> O_NONBLOCK to mq_open and be prepared for mq_send to return -1 with
>> errno set to EAGAIN/EWOULDBLOCK.
>>
>> Would this be your problem ?
> 
> Ok, I now have looked at your test code, you measure when posting the
> first message, and you already have O_NONBLOCK set. Could you try to
> create the queues in the reverse order and see what happens?

Also, would you have CONFIG_XENO_OPT_DEBUG_QUEUES activated ? In this
case, list operations are no longer O(1).

-- 
                                          Gilles