Jan Kiszka wrote:
Wolfgang Grandegger wrote:
Hello,

on the Xenomai mailing list the topic "bus error flooding" popped up
again. Various users reported trouble due to high bus error rates and
bad impact on latencies. Some discussion is going on on how to avoid
such flooding. I have already implemented "on-demand" bus error
interrupts. Bus error interrupts are then only enabled when at least one
socket is listening on bus errors. But flooding can still occur and we
are thinking about a better way of downscaling or temporarily disabling
them. Socket-CAN currently restarts the controller after 200 bus errors.
My preferred solution for RT-Socket-CAN currently is to stop the CAN
controller after a kernel configurable amount of successive bus errors.
More clever ideas and comments are welcome?

To have some input, I have measured the bus error rate with the PEAK
PCAN PCI card on my Icecube MPC5200 eval-board doing rtcansend without
cable connected. Here are the results for the various baud-rates:

   125 KB/s  1926 BEI/s
   250 KB/s  3925 BEI/s
   500 KB/s  7856 BEI/s
  1000 KB/s 15700 BEI/s

So bus errors come in at a rate comparable to shortest possible frames
at maximum speed, right? That's an IRQ load you can live with - if you
plan to load your CAN bus at 100% anyway. But if you don't...

Yes, it looks like.

The latency measured with "latency" from the testsuite reported an
increase of the latency with load from 67 to 95us almost independently
of the baud-rate. Sending messages with 8 byte payload from MSCAN to
SJA1000 on the same node as fast as possible increased the latency up to
103us. This measurement did not include delivery of messages to sockets
(actually no socket was listening).


Some dump of /proc/xenomai/stat would be interesting (system load in
both cases).

OK, here for bus error flooding at 1MB/s:

bash-2.05b# cat /proc/xenomai/stat
CPU  PID    MSW        CSW        PF    STAT       %CPU  NAME
  0  0      0          9781211    0     00500080   74.0  ROOT
  0  27199  130        264        0     00300182    0.0  display-27197
  0  27200  0          260166     0     00300184    8.1  sampling-27197
  0  0      0          29325916   0     00000000   14.5  IRQ0: SJA1000
  0  0      0          0          0     00000000    0.0  IRQ0: SJA1000
  0  0      0          1000002    0     00000000    0.0  IRQ55: MSCAN
  0  0      0          0          0     00000000    0.0  IRQ56: MSCAN
  0  0      0          9685429    0     00000000    3.0  IRQ256: [timer]

and here for "rtcansend -d 0 -l 1000000 rtcan0 1 2 3 4 5 6 7":

bash-2.05b# cat /proc/xenomai/stat
CPU  PID    MSW        CSW        PF    STAT       %CPU  NAME
  0  0      0          10377571   0     00500080   51.5  ROOT
  0  27199  336        816        0     00300182    0.0  display-27197
  0  27200  0          672738     0     00300184    5.8  sampling-27197
  0  29526  0          291678     0     00300182   23.6  rtcansend-29526
  0  0      0          30863047   0     00000000    9.7  IRQ0: SJA1000
  0  0      0          0          0     00000000    0.0  IRQ0: SJA1000
  0  0      0          1242608    0     00000000    6.5  IRQ55: MSCAN
  0  0      0          0          0     00000000    0.0  IRQ56: MSCAN
  0  0      0          10115159   0     00000000    2.1  IRQ256: [timer]

Wolfgang.


_______________________________________________
Xenomai-core mailing list
Xenomai-core@gna.org
https://mail.gna.org/listinfo/xenomai-core

Reply via email to