CPU Cost of having Posix API enabled if not used.

[Sebastian Huber]

Hello,

On 02/28/2013 05:26 PM, Tom Bojsen wrote:
> Hi,
>
> Does enabling the Posix interface cost extra CPU cycles if it is not used?

in your version, yes.  In the latest Git master branch, no.  The RTEMS and 
POSIX signals need a post thread switch extension.  See end of 
_Thread_Dispatch() (_API_extensions_Run_post_switch( executing )):

http://git.rtems.org/rtems/tree/cpukit/score/src/threaddispatch.c

In earlier RTEMS versions the post switch extension was installed during system 
start.  Now it is installed on demand.  On systems which frequently switch 
threads the post switch overhead is measurable.

http://git.rtems.org/rtems/commit/?id=ba3163131770e730cbf5168333c84daa57bc14e5
http://git.rtems.org/rtems/commit/?id=9465fca287e9417e05d2efe572d770fd60ad61db

An unused POSIX API adds also some dead code.

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber at embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.