Re: [Xenomai] xenomai/ipipe arm64 port

[Jorge Ramirez Ortiz <jro@xenomai.org>]

On 09/01/2015 02:27 PM, Dmitriy Cherkasov wrote:
> We have seen this before, but so far have not found a way to consistently
> reproduce it.
> 
> There are some caveats with the current way context switching is done in Xenomai.
> 
> On armv7, there was a completely separate implementation of xnarch_switch_to(),
> as well as separate fpu and TLS switching. At this stage for armv8 however, we
> are doing a direct call to the kernel's __switch_to(), which then performs the
> relevant register switches.
> 
> Another possibility is that this may be lurking in the mm switch. During calls 
> to check_and_switch_context(), the interrupt state may not always
> match what is expected according to the comments in the original
> version of that function. 
> 
> Overall, this mechanism could definitely benefit from further review.
> 


Thanks Dimitry.
I'll also try to look into this for this specific platform (however I am hopping
that either Gilles or Philippe can spend some time on this soon)

Just for completeness, as things stand this is pretty much that value I am
seeing over consecutive runs.

RTD|      4.167|      6.099|     11.667|       0|     0|      3.333|     66.667
RTD|      4.167|      6.217|     13.333|       0|     0|      3.333|     66.667
RTD|      4.167|      6.259|     11.667|       0|     0|      3.333|     66.667
RTD|      4.167|      6.226|     12.500|       0|     0|      3.333|     66.667
RTD|      4.167|      6.105|     11.667|       0|     0|      3.333|     66.667
RTD|      4.167|      6.181|     12.500|       0|     0|      3.333|     66.667
RTD|      4.167|      6.232|     12.500|       0|     0|      3.333|     66.667
RTD|      4.167|      6.483|     20.000|       0|     0|      3.333|     66.667
RTD|      4.167|      6.409|      9.167|       0|     0|      3.333|     66.667
RTD|      4.167|      5.707|     12.500|       0|     0|      3.333|     66.667
RTD|      4.167|      5.026|      6.667|       0|     0|      3.333|     66.667
RTT|  00:15:04  (periodic user-mode task, 1000 us period, priority 99)
RTH|----lat min|----lat avg|----lat max|-overrun|---msw|---lat best|--lat worst
RTD|      4.167|      5.025|      6.667|       0|     0|      3.333|     66.667
Load script terminated, terminating checked scripts
---|-----------|-----------|-----------|--------|------|-------------------------
RTS|      3.333|      6.540|     66.667|       0|     0|    00:15:04/00:15:04
pipe_in: /tmp/xeno-test-in-9797

-- 
jro