Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Andreas Glatz wrote:
>>> Hi Philippe,
>>>
>>> At the Xenomai Users Meeting last year I asked you if Xenomai would offer a 
>>> possibility to lower the priority of certain Xenomai tasks below that of 
>>> Linux. We need this feature since we have tasks in our RT application which 
>>> should only run when Linux is idle (A statistics collection task which part 
>>> of the RT application and hard to isolate from this application).
>>>
>> What prevents using a borderline thread (if you need to interact with
>> blocking Xenomai services) with SCHED_OTHER and a Linux nice level of 19?
> 
> Well, this does not really guarantee that the thread will run only when
> linux is idle. The thread will eat some cpu time, the nice level is not
> a strict priority, as you know.

Where do you really need anything stricter? It's the opposite of "I need
true 100% CPU for my task, and that forever."

> But in fact, I wonder why Andreas wants
> a new scheduling policy for xenomai, what is needed, is simply a
> SCHED_IDLE (maybe it exists ?!) policy for Linux.
> 

There is no such thing AFAIK. If you are concerned that some CPU
intensive low prio job eats too much CPU, you normally reduce its
nice-level and/or confine its CPU bandwidth via cgroups.

Jan

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