On Tue, 2012-09-11 at 13:38 +0200, Wolfgang Wallner wrote:

Hello all,

I have a few questions about the logging entry "sched: RT throttling
activated" which I observe, and hope this is the correct place to
ask :)
I will start by describing how i come to see this logging entry:

I use an industrial PC with an 2.6.33 RT PREEMP kernel to run a real
time application (based on the openPOWERLINK stack [1]), which
consists of a kernel part and a user space part.
My application uses the openPOWERLINK stack to exchange data with
other real time nodes in the network (a good overview how this is done
is given on wikipedia [2]).

When I let my application run overnight, I always see that it stops
working after some hours, and the output of dmesg shows the following:

[ 622.722690] EdrvInitOne waiting for link up...
[ 624.439269] EdrvInitOne finished with 0
[ 624.439334] EdrvInit local MAC = 00 60 65 06 B2 25 
[ 624.454662] EplApiProcessImageAlloc: Alloc(640, 1100, 2, 2)
[ 624.454672] EplApiProcessImageAlloc: Alloc(eeea2000, 640, eef36800,
1100)
[ 624.477242] ifconfig epl 192.168.100.240 returned 0
[ 635.058012] epl: no IPv6 routers present
[60382.945209] sched: RT throttling activated
[60382.945209] EplTimerHighResk: Continuous timer (handle 0x10000001)
had to skip 836 interval(s)!

Likely realtime task went gaga.  Kernel or userspace doesn't matter.

My questions are now:

* What does this logging entry mean?
   Could you please point me to some information about RT throttling
so that I can understand what's it about?

With stock settings, it means realtime task[s] consumed > 95% of the
throttle interval (1s), so the throttle activated, allowing SCHED_NORMAL
tasks to have a sip of CPU, to let you try to save the box from nutty RT
CPU hogs.  See kernel/sched_rt.c.

* How to debug this issue?
At the moment I don't know what is cause and what is effect.
I'm not sure if I have a misconfiguration somewhere on my linux system
and this influences my application or vice versa.

Any tips on how to find out what's going on are greatly appreciated :)

Hm, I would revoke godlike powers until the recipients can be trusted to
use them wisely.  100% CPU utilization being considered highly unwise.

-Mike