RTEMS vs Linux : Performance analysis : Comments and Suggestions Please

sashti srinivasan svasn_rtems at yahoo.com
Fri Mar 19 12:42:30 UTC 2004

> More details, please.
> Which CPU has been used?
      Lots of thanks for various suggestions.  I
compare linux running on x86 pc and rtems on the same
pc386(same machine).
  Linux Kernel : 2.4.18
  CPU          : Pentium III
  Clock speed  : 733 MHz

> How did you measure these figures?
    I wrote a program using POSIX api that repeats all
these operations a large number of times and took the
average.  For time measurement I used gettimeofday(). 
I learnt from Dr. Joel that this routine has only the
resolution of clock ticks.  And accurate routines
Timer_initialize and Read_timer did not work on PC386.
 Best support from list helped me read the hardware
8254 timer (counter0) to measure the time since last
tick.  If a tick occurs while reading the counter0, I
read counter0 again.

> Which compilers, which flags have been used to
> compile the Linux-Kernel,
> Linux-libc, Linux-application, RTEMS and your RTEMS
> application?
   glibc        : 2.2.93
   linux kernel : 2.4.18
   RTEMS        : 4.5 distributed with LECCS by
Gaisler Research.  I could not succeed in building
rtems 4.6.  Does it matter in a significant way for
pc386?  The error reported while building was someway
related to PTHREAD_CANCELLED macro.  I found somebody
reporting same problem in archives and also found the
reply suggesting to define PTHREAD_CANCELLED to
arbitrary value.  It was also said that it is a bad
idea to do so.  In order to be clear, I used 4.5 which
built successfully.

  I configured rtems in this manner:
   $(rtemssrc)/configure --target=i386-rtems 
--enable-rtemsbsp="pc386" --enable-posix=yes

> >  Please suggest some way of
> > improving the performance of rtems in these
> aspects.
> Number one source of improvement for RTEMS: The
> compiler flags.
> There, choosing the appropriate set of flags can
> result into huge
> differences in performance.
     I find it very difficult to follow the configure
scripts and makefiles.  Please guide me in setting the
compiler flags and also suggest me appropriate
compiler flags that will improve the performance.  

     If possible also guide me in generating configure
and Makefile.in from original scripts.  This will help
me in a great way in having a deep understanding of
components of rtems.  My understanding of autoconf and
automake is very poor.  Please forgive me for requests
unrelated to rtems.

     One more request:
> > (All Times are in microseconds : Average of some
> large
> > number of operations)
> > 
> >                               Linux   RTEMS
> >        Time To Lock a Mutex =  0.12   0.30
> >      Time To Unlock a Mutex =  0.12   0.28
> >      Initialize a Semaphore =  0.31   0.99
> >         Destroy a Semaphore =  0.10   1.46
> >              Semaphore Wait =  0.20   0.24
> >              Semaphore Post =  0.19   0.31
> These figures are no actual surprize to me, because
> Linux pthread
> implementation is pretty low-level, lean and highly
> optimized for speed,
> while RTEMS's pthreads/posix implementation is a
> wrapper to RTEMS native
> mechanisms and therefore is comparatively heavy
> weighted.
       Is it possible to improve the performance of
mutexes and semaphores in such a way that is close to
linux?  Please guide me in going about it.
> >      Thread Switching Time =  9.85   1.81
> Note this figure above. mutexes and semaphores are
> only one side of the
> medal ;)
> >     Please suggest some ideas regarding
> improvement of
> > mutex and semaphore performance of rtems.
> Ralf

With Best Regards

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