Re: [Xenomai-core] Xenomai latency tests on various PowerPC boards

[Philippe Gerum <rpm@xenomai.org>]

Wolfgang Grandegger wrote:
> Hallo,
> 
> attached you will find the results of Xemonai latency measurements on
> various embedded PowerPC boards using MPC 8xx and AMCC 4xx processors,
> from low to high end covering a worst case latency range from 25 to 225
> us. It also includes a comparison with RTAI 3.0r5 on the slowest CPU.
> Here are some remarks and comments:
> 
> - On low-end processor code size matters a lot and it's difficult to
>   beat RTAI/RTHAL.
>

Beat no, get closer, yes, probably. The good news is that looking at the 
figures, we do have a margin of improvement! :o>

Btw, the nucleus can be configured so that the user-space threading engine is 
compiled out (i.e. CONFIG_XENO_OPT_PERVASIVE from the nucleus menu), which would 
be the corresponding profile to compare with klatency (i.e. sched_up). Disabling 
this option reduces the code size for the nucleus from:

    text	   data	    bss	    dec	    hex	filename
   66740	    792	   6540	  74072	  12158	nucleus/xeno_nucleus.ko

to:

   text	   data	    bss	    dec	    hex	filename
   52596	    576	   3956	  57128	   df28	nucleus/xeno_nucleus.ko

Still a bit fat though.

> - Apart from the CPU power, big caches and a fast memory interface
>   improves latencies.
> 
> - L2 cache improves latencies a lot (compare Ocotea with Yosemite).
> 
> - I'm a bit puzzled about the results of the "cruncher" test. Could
>   someone explain the output, please?
> 

This test is reminiscent of the HYADES project (ia64 port of RTAI/fusion), where 
we wanted to illustrate the level of execution determinism one could achieve 
using the interrupt shield technique on large ia64 SMP systems. To this end, we 
measured the jitter in execution time of a calibrated float-crunching loop, with 
and without interrupt load. This test is likely going to disappear at some point 
in time, because it's not that informative in Xeno's context.

> - Stability seems already quite good. At least I did not observe any
>   crash yet :-).
> 

That's cool. I see no other way to properly improve performances than first 
having something which could be run on various platforms without them randomly 
jumping out of the window, or us relying on plain Voodoo stuff to explain why 
those setup would work or not.

> The PowerPC port of Xenomai is already in good shape. That's great!
> 

Thanks. This is likely because I do feel better since I have been aware that 
there's life beyond x86. :o)

> Wolfgang.
> 
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
> Latency tests with Xenomai on various PowerPC boards
> ----------------------------------------------------
> 
> Board   : Processor  CPU-Clk Bus-Clk I-Cache D-Cache Memory Remarks
> 
> TQM860L : MPC 860     50 MHz  50 MHz    4 KB    4 kB  16 MB
> TQM866M : MPC 866    133 MHz  66 MHz   16 KB    8 kB 128 MB
> 
> Walnut  : AMCC 405GP 200 MHz 100 MHz   16 KB    8 kB  32 MB
> Yosemite: AMCC 440EP 533 MHz 133 MHz   32 KB   32 KB 256 MB DDR-RAM, FPU
> Ocotea  : AMCC 440GX 533 MHz 152 MHz   32 KB   32 KB 256 MB DDR-RAM, L2 256 KB
> 
> 
> Linux  : DENX linux-2.6.14-rc3-g4c234921
> iPipe  : 1.0-00
> Xenomai: SVN 2005-10-15
> 
> 
> CRUNCER without load:
> 
>          | Ideal computation time
> TQM860L  |   368 us ???
> TQM866L  | 10008 us 
> Walnut   | 10150 us
> Yosemite |  9911 us
> Ocotea   |  9479 us 
> 
> 
> SWITCH without load:
> 
>          |     lat min|     lat avg|     lat max|        lost
> TQM860L  |      103360|      107840|      209280|           0
> TQM866L  |       25745|       31880|       51369|           5
> Walnut   |       24620|       25965|       32280|           1
> Yosemite |        5626|        5655|       17403|           0
> Ocotea   |        5158|        5169|       10038|           0
> 
> 
> KLATENCY with load:
> 
>          |-----lat min|-----lat avg|-----lat max|-overrun|---test-time
> TQM860L  |       50560|       98976|      199040|       0|    00:09:45
> TQM866L  |       13835|       28571|       74348|       0|    00:11:44
> Walnut   |       16195|       25062|       45755|       0|    00:10:09
> Yosemite |        3106|        9697|       36832|       0|    00:09:55
> Ocotea   |        3575|        7438|       24474|       0|    00:10:50
> 
> 
> LATENCY with load:
> 
>          |-----lat min|-----lat avg|-----lat max|-overrun|---test-time
> TQM860L  |       60480|      120960|      224320|       0|    00:09:46
> TQM866L  |       15759|       34286|       78799|       0|    00:11:14
> Walnut   |       21070|       31650|       64500|       0|    00:09:58
> Yosemite |        3808|       12163|       47898|       0|    00:10:00
> Ocotea   |        3575|        7438|       24474|       0|    00:10:50
> 
> 
> KLATENCY comparison Xenomai 2.0 vs. RTAI/RTHAL 3.0r5 on TQM860L:
> ---------------------------------------------------------------
> 
> KLATENCY with load:
> 
>             |-----lat min|-----lat avg|-----lat max|-overrun|---test-time
> Xenomai 2.0 |       50560|       98976|      199040|       0|    00:09:45
> RTAI 3.0r5  |       23120|       31838|       70520|       ?|    00:12:26
> 
> 
> 
> Note: load has been put onto the system by running in a telnet session
>       "ping -f <remote-host-ip>" and "while ls; do ls; done".
> 
> Note: all test have been run with CONFIG_XENO_HW_TIMER_LATENCY="1" and
>       CONFIG_XENO_HW_SCHED_LATENCY="1" to get correct latancy values.
>       RTAI figures have been corrected manually.
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
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-- 

Philippe.