[Xenomai-help] Cast a double value fails

[Xenomai-help] Cast a double value fails

[Bertram Stemer]

Hi,
I'm using Xenomai 2.5.6 with Linux 2.6.36 on a PowerPC and 
have written a real-time application that runs on an isolated
CPU (Kernel option isolcpus). When I start this application on 
another core, where a plain Linux application runs I get 
sporadically unexpected results in the non real-time application, 
when casting a double to an integer?!

To reproduce this behavior I have a small non real-time test
application that runs in parallel to the RT application:
...
while (1) {
	int z = 4.0;
	if (z != 4)
		printf("cast error detected!");
	/* sleep some microseconds */
}
...
 
Does anyone know how this can happen? Is there a CPU utilization
bound for real-time applications that run on the same CPU with 
plain Linux tasks?

Thanks in advance,
Bertram

Re: [Xenomai-help] Cast a double value fails

[Philippe Gerum]

On 03/07/2012 12:46 PM, Bertram Stemer wrote:
> Hi,
> I'm using Xenomai 2.5.6 with Linux 2.6.36 on a PowerPC and
> have written a real-time application that runs on an isolated
> CPU (Kernel option isolcpus). When I start this application on
> another core, where a plain Linux application runs I get
> sporadically unexpected results in the non real-time application,
> when casting a double to an integer?!
>
> To reproduce this behavior I have a small non real-time test
> application that runs in parallel to the RT application:
> ...
> while (1) {
> 	int z = 4.0;
> 	if (z != 4)
> 		printf("cast error detected!");
> 	/* sleep some microseconds */
> }
> ...
>
> Does anyone know how this can happen? Is there a CPU utilization
> bound for real-time applications that run on the same CPU with
> plain Linux tasks?

isolcpus does not actually fully isolates CPU from non-rt activity. What 
you see is likely a bug in the Xenomai core, leaking fpu context bits 
spuriously between -rt and non-rt. Adding this to the todo list.

>
> Thanks in advance,
> Bertram
>
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> Xenomai-help mailing list
> Xenomai-help@domain.hid
> https://mail.gna.org/listinfo/xenomai-help
>


-- 
Philippe.