IRQ latency (was Re: RTEMS-MVME5500 BSP v1.3 available)

Kate Feng feng1 at
Tue Aug 9 18:49:58 UTC 2005

"Joel Sherrill " wrote:

> Do you know the difference between your 1.3 and what is on the
> 4.6 branch?

The difference is in the ChangeLog.

> Kate Feng wrote:
> > I will try to sync with the current CVS and new tools as soon as I
> > managed to get more disk space on my PC.
> > As I was passing by the New York city last week, I started to think that
> > one might get better  performace on IRQ latency  and context switch
> > using the new powerPC shared files and new compiler.
> You mean it might be possible to squeeze even more performance out of
> this BSP? :)  It is already doing well in the benchmarks.

If you think it's already doing well, then I probably do'nt have to
try the RTEMS4.7.

I thought  there is some discrepancy between my result and Peter's.
It  seems to me the following description  uses interrupts.

Peter Dufault wrote :
> Data acquisition interrupt (copies data off PCI board, posts
> semaphore): 22KHz 15KHz

The former one is for RTEMS and the later one is for vxWorks.
RTEMS  interrupt outperformed vxWorks by 30%, which I  interprete
it as the "average case" instead of the "worst case".  However,
looking at the  average performance I got   even for  the loaded
system (attached at the end), it seems that RTEMS is 30%
slower on the "average" case.  This puzzles me.   The difference
between my RTEMS system and his is :

1. RTEMS4.6  with gcc-3.2  v.s. RTEMS4.7 with gcc-4.0
2. optimized v.s. non-optimized.
3. system bus counter's IRQ v.s. PMC module's IRQ, which should
not make a difference for the optimized version.
4. native O.S. thread v.s. pthread for the benchmark software.

Friday, July 29:
MVME5500    Interrupt   Latency    |   Context Switching
                     max      (average)         |     max    (average)
Idle System:

RTEMS        5.04       (3.45)            |    6.80     (0.96)

vxWorks      6.10       (1.58)            |    9.65     (0.91)

Loaded System:

RTEMS        8.17       (3.74)            |   17.48     (1.69)

vxWorks     13.90       (1.68)           |   20.80     (1.90)

** All units are in usec.


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