RTEMS vs Linux : Performance analysis : Comments and Suggestions Please

Ralf Corsepius ralf_corsepius at rtems.org
Fri Mar 19 10:49:53 UTC 2004

On Fri, 2004-03-19 at 10:47, sashti srinivasan wrote:
> Hello All,
>        Because of the full fledged support from the
> list, I am now able to measure time accurately with 1
> microsecond accuracy on PC386.  I have got some
> figures of merit, based on this I want to improve the
> performance of rtems.  Here are the results for
> discussion.  This is a comparison between linux and
> rtems on pc386 platform.  POSIX api is used for the
> measurement and to the best possible extent same code
> has been used in both. 

More details, please.

How did you measure these figures?

Which CPU has been used?

Which compilers, which flags have been used to compile the Linux-Kernel,
Linux-libc, Linux-application, RTEMS and your RTEMS application?

>  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.

> (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.

>      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.


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