Re: [Xenomai-help] AT91SAM9260 latency

[Juan Antonio Garcia Redondo <juan-antonio.garcia@domain.hid>]

On 23/01/08 14:15, Gilles Chanteperdrix wrote:
> On Jan 23, 2008 11:04 AM, Gilles Chanteperdrix
> <gilles.chanteperdrix@xenomai.org> wrote:
> > On Jan 23, 2008 7:52 AM, Juan Antonio Garcia Redondo
> >
> > <juan-antonio.garcia@domain.hid> wrote:
> > > I see everything OK except for the first samples of cyclictests. Any comments ?
> >
> > The load you apply does not load the cache, which is a source of
> > jitter. You should run the cache calibrator (I do not find the cache
> > calibrator URL, but it is somewhere in Xenomai distribution or wiki).
> 
> It is in the TROUBLESHOOTING guide, question "How do I adequately stress test".
> 
> -- 
>                                                Gilles Chanteperdrix

Thanks Gilles, I've done more tests using the cache calibrator from
http://www.cwi.nl/~manegold/Calibrator. The latency numbers are very
similar althought I've found an strange behaviour related to telnet
sessions.

Environment:
	o Tests running from console over atmel serial port.
	o A telnet session over on-chip ethernet. 
        o System without load.

./latency -p 500 -t0
== All results in microseconds
warming up...
RTT|  00:00:01  (periodic user-mode task, 500 us period, priority 99)
RTH|-RTH----lat min|-----lat avg|-----lat max|-overrun|----lat best|---lat
worst
RTD|      49.613|      52.190|      62.822|       0|      49.613| 62.822
RTD|      42.203|      52.512|      66.365|       0|      42.203| 66.365


Now If hit a key on the telnet session :

RTD|      36.726|      57.989|     109.536|       0|      31.572| 109.536  <-------- Here I've hit the key.
RTD|      36.404|      51.868|      69.587|       0|      31.572| 109.536
RTD|      35.760|      51.868|      73.775|       0|      31.572| 109.536

Now, I launch an script which executes four instances of cache
calibrator.

RTD|      45.103|      57.667|      75.708|       0|      32.538| 122.422
RTD|      45.425|      57.023|      76.030|       0|      32.538| 122.422
RTD|      46.069|      57.023|      75.708|       0|      32.538| 122.422

Now, I can hit a key on the telnet session without effects over latency
numbers:

RTD|      44.136|      57.989|      75.386|       0|      27.384| 128.221
RTD|      46.713|      57.345|      76.353|       0|      27.384| 128.221
RTD|      44.780|      57.345|      76.675|       0|      27.384| 128.221
RTD|      43.492|      56.701|      76.997|       0|      27.384| 128.221

Now I stop the calibrator process and launch 'ping -f -s2048 192.168.2.82' from an external
machine.

RTD|      40.270|      68.621|      90.850|       0|      27.384| 128.221
RTD|      36.082|      68.621|      88.273|       0|      27.384| 128.221
RTD|      40.592|      67.976|      91.494|       0|      27.384| 128.221
RTD|      41.237|      68.298|      89.239|       0|      27.384| 128.221


Now If hit a key on the telnet session :

RTD|      42.203|      67.976|      88.273|       0|      27.384| 128.221
RTD|      32.216|      93.427|     128.543|       0|      27.384| 128.543 <---------- Here I've hit the key.
RTD|      42.203|      68.298|      87.628|       0|      27.384| 128.543

And again the calibrator execution results on eliminate the strange
behaviour whith the telnet session.

Any clues ?

BTW, if finally the bad numbers on ARM are user-context switches related,
are you considering the ipipe upgrading to 2.6.23 ? 

Regards,
	Juan Antonio