SRU Bug #229499

[Alessio Igor Bogani]

Hi Kernel Team,

SRU Justification:

Bug Description: Recently i have worked on just upgraded Hardy
systems.I have noticed that there is a don't clearly visible
regression about rt kernel flavour. It seems that on 2.6.24 the
Dynamic Ticks features is incompatible with CONFIG_PREEMPT_RT. This
cause huge latency and it is a regression respect Gutsy!

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 at 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 at 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

For this reason please pull:
The following changes since commit 45a2f1fa59db5a20f63cd3f120cf5df5f51d0e0b:
  Tim Gardner (1):
        UBUNTU: V4L/DVB (7132): Add USB ID for a newer variant of
Hauppauge WinTV-HVR 900

are available in the git repository at:

  git://kernel.ubuntu.com/abogani/ubuntu-hardy-rt.git master

Alessio Igor Bogani (1):
      UBUNTU: rt: Disable Dynamic Ticks (CONFIG_NO_HZ)

 debian/binary-custom.d/rt/config.amd64 |    7 ++-----
 debian/binary-custom.d/rt/config.i386  |    7 ++-----
 2 files changed, 4 insertions(+), 10 deletions(-

Thanks!

Ciao,
Alessio