Re: [Xenomai-main] Bug in xenomai on top of POSIX

[Gilles Chanteperdrix]

address@hidden wrote:
 > En réponse à Gilles Chanteperdrix <address@hidden>:
 > 
 > > 
 > > Any feedback on this newer version will be appreciated.
 > We will use xenomai on top of posix heavly, so i will send you feedback...
 > 

I did not make it clear in my previous mail, but I advise you not to
start a new project using Xenomai on top of POSIX. Even if all the bugs
were corrected, this layer has a lot of deficiencies which can not be
corrected :
1- you can not hope for a tick timer frequency greater than a few tens of
  hertz, even when using SCHED_FIFO scheduling policy, and the
  theoretical limit is Linux tick timer frequency, 100 Hz by default,
  without accounting for the jitter ; 
2- the nucleus (the Xenomai core) needs to schedule its threads itself
  and the POSIX threads interface is made to let the kernel schedule your
  threads, so POSIX threads are not adapted to RTOS emulation, which
  leads to the current heavy-weight, unefficient Xenomai POSIX layer ;
3- as Linux scheduler is totally unaware of Xenomai, using Linux blocking
  syscalls does not lead to cooperative scheduling, all your threads are
  blocked.

I think these deficiencies are among the reasons why the Xenomai POSIX
layer was discontinued.

Let's make it clear : the posix.h in the cvs is only a bugfix release
for the unlucky who would have already started using the POSIX layer.

Regards.

-- 


                                            Gilles Chanteperdrix.