Jan Kiszka wrote:
> Jan Kiszka wrote:
>> Gilles Chanteperdrix wrote:
>>> Jan Kiszka wrote:
>>>> 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.
>>> SCHED_IDLE exists.
>>>
>> Ah, as "nice 20". Same mechanism, just another level.
>>
>
> ...and before trying something else:
>
> "SCHED_IDLE: This is even weaker than nice 19, but its not a true
> idle timer scheduler in order to avoid to get into priority
> inversion problems which would deadlock the machine."
Mmmm, priority inversion? I thought the kernel had priority inheritance?
--
Gilles.
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