[Xenomai-help] question about the latency test running on Blackfin

[adam li <yi.li@domain.hid>]

Hi,

I tried to run the "latency" test on Blackfin 533-STAMP board, in
different modes. Here is the output of the test result:

(I am using xenomai-2.1.0 with default configuration,(adding "timer
benchmark" driver)).

1. # latency -h -t0 -T30
HSH|--param|--samples-|--average--|---stddev--
HSS|    min|        29|      9.862|      0.581
HSS|    avg|    299964|     11.380|      2.676
HSS|    max|        29|     49.759|      5.296

# cat /proc/xenomai/stat
CPU  PID    MSW        CSW        PF    STAT      NAME
  0  0      0/0        288239     0     00400080  ROOT
  0  47     23/22      145        0     00300082  display
  0  48     1/0        220501     0     00300084  sampling


2. # latency -h -t1 -T30
HSH|--param|--samples-|--average--|---stddev--
HSS|    min|        29|      6.552|      0.686
HSS|    avg|    299985|      8.849|      1.601
HSS|    max|        29|     35.379|      6.383

cat /proc/xenomai/stat
CPU  PID    MSW        CSW        PF    STAT      NAME
  0  0      0/0        436079     0     00400080  ROOT
  0  58     6/5        42         0     00300082  display
  0  0      0/0        57685      0     00000084  timerbench


3. # latency -h -t2 -T30
== Sampling period: 100 us
== Test mode: in-kernel timer handler
== All results in microseconds
warming up...
RTT|  00:00:01  (in-kernel timer handler, 100 us period)
RTH|-----lat min|-----lat avg|-----lat max|-overrun|----lat best|---lat
worst
RTD|      -5.340|      -4.385|       8.064|       0|      -5.340|
8.064
RTD|      -6.848|      -4.359|       8.907|       0|      -6.848|
8.907
RTD|      -6.443|      -4.518|      23.878|       0|      -6.848|
23.878
RTD|      -5.757|      -4.240|      23.377|       0|      -6.848|
23.878
RTD|      -6.153|      -4.144|      24.107|       0|      -6.848|
24.107
RTD|      -5.446|      -4.040|      18.754|       0|      -6.848|
24.107
RTD|      -7.697|      -4.690|      20.319|       0|      -7.697|
24.107

HSH|--param|--samples-|--average--|---stddev--
HSS|    min|        29|      5.621|      0.820
HSS|    avg|    299979|      3.990|      0.774
HSS|    max|        29|     15.966|      6.248


And my questions are:

1). Compared the output of Mode 0 (user space task) and Mode 1 (kernel
space task), the average latency of Mode 1 is shorter. In Mode 1, the
"timerbench" thread is running in primary mode, but what makes the
latency in secondary mode longer?

2) From the output of Mode 0, the "MSW" field of "sampling" thread is
always 1/0, does that mean the "sampling" thread will switch to primary
mode and keep stay in primary mode throughout the test?

3) In Mode 2 (timer handler in kernel space), the "lat min" and "lat
avg" is negative, is this correct? If it is correct, why the latency is
much shorter than mode 1(kernel space task)?

And finally a general question:
4) why there is RTDM? What is the design purpose? If I were to write
Realtime device drivers, shall I use RTDM?


Thanks,

-Li Yi