[Xenomai-core] native rt_timer questions

[Xenomai-core] native rt_timer questions

[Fillod Stephane]

Hi!

Why rt_timer functions, esp. rt_timer_tsc(), are not inlined in
user-space 
(with CONFIG_XENO_HW_DIRECT_TSC) ? Is it because some policy insists 
that every library function must have an overridable symbol?
Even a branch is worrisome when doing repetitive micro-measurements.
What about a patch along the following? or an extern inline?

--- include/native/timer.h     15 May 2008 07:40:30 -0000
+++ include/native/timer.h     3 Sep 2008 09:10:31 -0000
@@ -46,7 +52,7 @@
 extern "C" {
 #endif
-#if (defined(__KERNEL__)  || defined(__XENO_SIM__)) &&
!defined(DOXYGEN_CPP)
+#if (defined(__KERNEL__)  || defined(__XENO_SIM__) ||
defined(__NATIVE_INLINE)) && !defined(DOXYGEN_CPP)
 static inline SRTIME rt_timer_ns2tsc(SRTIME ns)
 {
        return xnarch_ns_to_tsc(ns);

BTW, I had the bad surprise of rt_timer_read() doing a syscall, which
is costly when doing fine measurement. Should it be documented?


The native rt_timer functions are documented in two locations:
http://www.xenomai.org/documentation/branches/v2.4.x/html/api/include_2n
ative_2timer_8h.html
http://www.xenomai.org/documentation/branches/v2.4.x/html/api/group__nat
ive__timer.html

Could they be gathered, maybe with the here below patch (untested, no
doxy expert):

--- include/native/timer.h     15 May 2008 07:40:30 -0000
+++ include/native/timer.h     3 Sep 2008 09:10:31 -0000
@@ -17,6 +17,8 @@
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.
+ *
+ * \ingroup native_timer
  */

 #ifndef _XENO_TIMER_H
@@ -26,6 +28,10 @@

 #define TM_ONESHOT XN_APERIODIC_TICK

+/** Structure containing timer-information useful to users.
+ *
+ *  @see rt_timer_inquire()
+ */
 typedef struct rt_timer_info {

     RTIME period;      /* !< Current status (unset, aperiodic, period).
*/

-- 
Stephane

Re: [Xenomai-core] native rt_timer questions

[Gilles Chanteperdrix]

Fillod Stephane wrote:
> Hi!
> 
> Why rt_timer functions, esp. rt_timer_tsc(), are not inlined in
> user-space 
> (with CONFIG_XENO_HW_DIRECT_TSC) ? Is it because some policy insists 
> that every library function must have an overridable symbol?
> Even a branch is worrisome when doing repetitive micro-measurements.
> What about a patch along the following? or an extern inline?
> 
> --- include/native/timer.h     15 May 2008 07:40:30 -0000
> +++ include/native/timer.h     3 Sep 2008 09:10:31 -0000
> @@ -46,7 +52,7 @@
>  extern "C" {
>  #endif
> -#if (defined(__KERNEL__)  || defined(__XENO_SIM__)) &&
> !defined(DOXYGEN_CPP)
> +#if (defined(__KERNEL__)  || defined(__XENO_SIM__) ||
> defined(__NATIVE_INLINE)) && !defined(DOXYGEN_CPP)
>  static inline SRTIME rt_timer_ns2tsc(SRTIME ns)
>  {
>         return xnarch_ns_to_tsc(ns);

I am afraid we do not want this on every architecture. On ARM where the
tsc is an emulation and contains a fair number of instructions using a
fair number of registers (still faster than a syscall, of course), I
think we do want an out of line function.

> 
> BTW, I had the bad surprise of rt_timer_read() doing a syscall, which
> is costly when doing fine measurement. Should it be documented?

I suggested once to use the tsc as well for the implementation of
clock_gettime(CLOCK_REALTIME) (the posix equivalent of rt_timer_read()),
but was told at the time that we may want, one day, to provide syscalls
to compensate for clock drifts, so reading the system clock should
remain a syscall.

-- 
                                                 Gilles.

Re: [Xenomai-core] native rt_timer questions

[Gilles Chanteperdrix]

Fillod Stephane wrote:
> The native rt_timer functions are documented in two locations:
> http://www.xenomai.org/documentation/branches/v2.4.x/html/api/include_2n
> ative_2timer_8h.html
> http://www.xenomai.org/documentation/branches/v2.4.x/html/api/group__nat
> ive__timer.html
> 
> Could they be gathered, maybe with the here below patch (untested, no
> doxy expert):

Fixed, thanks ! But your MUA mangles patches (by adding newlines), so,
you should rather send them as attachments.

-- 
					    Gilles.