[Xenomai] Build Xenomai Lib native on the Beaglebone Black

Yogi A. Patel yapatel at gatech.edu
Sun Mar 16 22:37:26 CET 2014

Hi Gilles -

Thanks for this information - this is great and provides a good comparison. I am getting about 40us on my beaglebone black running debian+xenomai 2.6.3. Disabling the L2 cache write-allocate bit to get 10us would be phenomenal. 

Question - what is the option to deselect in the “make menuconfig” to disable the L2 cache write-allocate bit?

I’ll post any results I have for comparison, if it helps.

Yogi A. Patel
(c): (828) 291-6715
(url): www.yapatel.org | @yapatel525

On Mar 12, 2014, at 8:29 AM, Gilles Chanteperdrix <gilles.chanteperdrix at xenomai.org> wrote:

> On 03/12/2014 12:59 AM, Yogi A. Patel wrote:
>> Flavio -
>> Would you mind sharing what latencies you are seeing on your Beaglebone black with xenomai?
> Some results which might be interesting, the results for the IGEPv2
> board, using an omap3630 processor, close to the beaglebone black
> processor, are in the 40-45us range, if the kernel is compiled with the
> right options, that is:
> - kernel built using thumb2 and optimized for size
> - preemption set to CONFIG_PREEMPT_NONE
> - CONFIG_SMP disabled
> - stack unwinding enabled
> - xenomai unlocked switch disabled
> - all xenomai/ipipe debugs off, except maybe "watchdog support" and
> "detect mutexes held in relaxed sections", as they should not incur an
> increase in latency.
> Since the I-pipe core series (so since linux 3.2), I have started
> recording the results I get on the test platforms I have, see, to show
> the improvements over time (most improvements are due to configurations
> changes):
> http://xenomai.org/~gch/core-3.2-latencies/
> http://xenomai.org/~gch/core-3.4-latencies/
> http://xenomai.org/~gch/core-3.5-latencies/
> http://xenomai.org/~gch/core-3.8-latencies/
> http://xenomai.org/~gch/core-3.10-latencies/
> Note that we recently discovered that disabling the L2 cache
> "write-allocate" bit on imx6 and omap4, so probably on any multi-core
> cortex a9, improved latencies considerably, and that moving the
> spinlocks code out-of-line did too, see:
> http://sisyphus.hd.free.fr/~gilles/panda-test/inline-spinlocks.png
> The change of the L2 write-allocate bit will be in the next Xenomai 2.x
> release, whereas the change of spinlock code will only appear in xenomai
> 3.0.
> Anyway, I would like to also try disabling the L2 cache write-allocate
> on omap3, but IGEPv2 is running in secure mode, so I can not change this
> configuration, I would probably need an "smc" call, but I have not found
> a documentation for these calls, so if anyone knows where to find this
> info, I am interested.
> Regards.
> -- 
>                                                                Gilles.

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