Messages in this thread |  | | | Date | Mon, 27 Dec 2010 12:13:42 +0530 | | Subject | Re: Sending some form of notifaction when sched_fifo throttling kicks in... | | From | Bharata B Rao <> |
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On Thu, Dec 23, 2010 at 6:47 PM, Dario Faggioli <raistlin@linux.it> wrote: > On Thu, 2010-12-23 at 12:39 +0100, torbenh wrote: >> hi... >> > Hi, > >> when the rt_runtime budget is exceeded, the kernel silently stops >> scheduling RT tasks. there is no way to distinguish this from >> a task taking very long to complete. >> > Well, this depends on how you do the accounting in your (user-level) > code. > >> it would be very nice, if the kernel would send some form of notifaction >> when it starts throttling things. >> > This might be tricky, if the meaning is signals or something to the > throttled tasks, since you can have a (or more!) runqueue full of > them... Are we signalling them all? Moreover, they'll get the > notification only after resuming, and it's not guaranteed that this > helps in finding out who is "responsible for" the throttling and... By > the way... > >> recording the timestamp of the last occurence of throttling >> in a /proc file would be sufficient, if there were no cgroups. >> >> would it be possible to add a readonly property to the cpu subsystem ? >> > ... If you think you're fine with some /proc (and perhaps cpuacct, if > cgroups are being used) readable, I can try to come up with something. > > I think that the number of times that throttling fired and the last > throttling instant could be exported this way without much issues. > > Do others have some idea and/or comments about that? This is > ABI/interface, and that really scares me! :-P
You might want to note that CFS bandwidth control patches export some such stats via a new per-cgroup file cpu.stat. It exports 3 statistics:
nr_periods: Number of enforcement intervals that have elapsed. nr_throttled: Number of times the group has been throttled/limited. throttled_time: The total time duration (in nanoseconds) for which the group remained throttled.
Regards, Bharata.
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