[Xenomai-core] rtdm timers

[Xenomai-core] rtdm timers

[Steven Seeger]

Gilles believes he's on the track of our FPU issue when using kernel  
threads. Would using an RTDM timer to accomplish our need have the  
same issue? We would not use the FPU in the timer of course, because  
it is not allowed.

I just don't want to spend the time converting things if it won't  
help. Does the list think it would be a worthwhile effort?

Thanks,
Steven

Re: [Xenomai-core] rtdm timers

[Gilles Chanteperdrix]

Steven Seeger wrote:
> Gilles believes he's on the track of our FPU issue when using kernel  
> threads. Would using an RTDM timer to accomplish our need have the  
> same issue? We would not use the FPU in the timer of course, because  
> it is not allowed.
> 
> I just don't want to spend the time converting things if it won't  
> help. Does the list think it would be a worthwhile effort?

We can not say for sure as long as we know what the bug is. But if it
is, as I suspect, a bug in the FPU switching logic for non-fxsr x86_32
cpus, you will not have it with a timer: when the timer fires, there is
no context switch and because of that you should have a lower latency
and a lower overhead of the driver using the timer (the downside, of
course, is that you can not call a function which sleeps). I do not know
however if it makes much difference on x86, to have an idea, compare the
output of klatency -t 1 and klatency -t 2.

-- 
					    Gilles.