Comment 1 for bug 229499

SRU Justification:

Impact: That bug affect all rt kernel flavour users. From a realtime point of view this is a severe regression.

Fix Description: To prevent this latency we need to disable Dynamic Ticks.

Patch is very simple and safe (one line in rt kernel configuration):
http://kernel.ubuntu.com/git?p=abogani/ubuntu-hardy-rt.git;a=commit;h=f80aed2d95a5be145a31b80d30fad86672b16e8c

Drawback: A bit more power consumption.

TEST CASE: I was able to put problem clearly visible using cyclictest, a realtime kernel test utility, on a couple of systems.
[Dynamic Ticks on]
abogani@picasso:~/WIP/rt-tests$ sudo ./cyclictest -t1 -n -p99 -q -l200000
T: 0 ( 7140) P:99 I:1000 C: 200000 Min: 4 Act: 40 Avg: 65 Max: 12047

[Dynamic Ticks off]
abogani@picasso:~/WIP/rt-tests$ sudo ./cyclictest -t1 -n -p99 -q -l200000
T: 0 ( 6481) P:99 I:1000 C: 200000 Min: 2 Act: 6 Avg: 6 Max: 321