On 05/26/2011 07:28 PM, Jonas Witt wrote:
> Hi all,
>
> i am having a problem concerning the clock drift under load:
>
> # /usr/xenomai/bin/clocktest
> == Tested clock: 0 (CLOCK_REALTIME)
> CPU ToD offset [us] ToD drift [us/s] warps max delta [us]
> --- -------------------- ---------------- ---------- --------------
> 0 775571614.0 166776.858 0 0.0
>
>
> It remains in the hundreds of MILLIseconds, changing constantly. My
> setup consists of an embedded Intel Atom board (1.6GHz Z530 processor)
> with a 2.6.32.7 kernel and Xenomai 2.5.2.
Hi Jonas,
Could you try and see if 2.5.6 with latest I-pipe patches has the same
behaviour?
> Latencies under load are
> reasonable. Mean latency < 10us. Maximum latency < 40us.
>
> Without load the ToD offset is approximately constant over time with a
> ToD drift in the range of 10 microseconds (strangely after a while this
> settles in a range of 2 microseconds). Does anyone have an idea how this
> can be caused?
First, I am not sure clocktest is meant to be use under load. Second,
does your system uses ntp?
> As a workaround I currently use rt_timer_read() in all
> relevant programs (also the non-realtime ones), since I need consistent
> timestamps between realtime and non-realtime tasks.
In order to solve this particular issue, we have a solution, but not yet
in stable released versions.
>
> One other (maybe unrelated) strange behavior is occasional secondary
> mode switches when calling rt_queue_read(...).
For this error, we need more details, such as a simple test case
allowing to reproduce the issue, and again, you need to be sure to
reproduce the issue on latest stable release with latest I-pipe patches.
Regards.
--
Gilles.
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