Re: Latest PreemptRT patch error on imx35

[Carsten Emde <Carsten.Emde@osadl.org>]

Tim,

> I just bootet 2.6.31-rc8-rt9 on the phycore-imx35 development board, 
> without any additional patches. The FEC Ethernet Controller went belly 
> up, but the system booted nevertheless. I tried cyclictest:
> root@pmx:~ cyclictest -t1 -p 80 -n -i 10000 -l 10000
As a role of thumb, the -i option is normally set to twice the expected
latency. If, for example you expect 100 us, set it to -i200. Your loop
end is then reached 50 times faster, or - what is much better - you may
specify 50 times more loops for a test of the same duration which
considerably increases the quality of your assessment. Normally,
however, you would probably wait for 100 million or even a billion loops.

> 0.05 0.10 0.05 1/39 570
> T: 0 (  570) P:80 I:10000 C:  10000 Min:     14 Act:   20 Avg:   19 Max:      27
> These  are Numbers from an Idle Machine (no network), but they look really good.
With an average of 19 and a maximum of 27, the result is probably not
very relevant. This indicates that the CPU was idle most of the time
when the wakeup occurred - every OS can do this. The challenge of an
RTOS is to wakeup in time also when the kernel is not idle, e.g. from
kernel or driver code while a lock is held. Therefore, adequate stress
tools must be running during a latency measurement.

> They are much better than my last tests on the imx31 with an older preemptrt-kernel 
> (2.6.29) which had idle latencys up to 80µs. 
> Given the fact, that ftrace is enabled, this is really impressive progress!
Please keep in mind that ftrace configured is not ftrace enabled. To
enable it, use cyclictest's -f option or execute
  echo function >/sys/kernel/debug/tracing/current_tracer
  echo 1 >/sys/kernel/debug/tracing/tracing_enabled
from command line.


I hope that this hasn't tempered your joy with your new hardware.

	Carsten.
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html