Re: strange scheduling latency results

BTW: in my answer I assumed that your latency test has the capability of 
measuring latency against a single source.
Therefore, it is out of scope if the latency is measured as in RTAI 
latency tests.
Paolo

On 04/12/2017 12:30 AM, Sebastian Kuzminsky wrote:
> Hi there, a LinuxCNC user reports strange thread scheduling results on 
> an AMD A6-6400K.  This is with RTAI 3.9 and Linux 3.4.55, compiled for 
> i686 (32-bit x86 mode).  Other hardware runs this exact software 
> without the strange behavior described below.
>
> There are two realtime threads in this system, which we call the "base 
> thread" and the "servo thread".  The base thread runs with a 25 
> microsecond period, the servo thread with a 1 millisecond period.
>
> We have a test program called "latency-histogram" that runs the 
> threads and monitors scheduling latency, and presents the results as a 
> graphical histogram.  Here's a graph from this A6-6400K machine:
>
> https://imagebin.ca/v/3IkSuxnTVoWH
>
> Notice that the base thread (on the left) runs about when it's 
> scheduled, with a bell-shaped curve of jitter around the "0 
> microseconds of latency" point.
>
> But the servo thread histogram (on the right) looks different.  It too 
> has a bell curve of scheduling jitter, but it's not centered on 0.  It 
> looks like the servo thread consistently starts a handful of 
> microseconds before it's supposed to.
>
> Any suggestions for us to debug or deal with this issue?
>
>

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