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." Jan
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