SRU Bug #229499

[Tim Gardner]

Tim Gardner wrote:
> Alessio Igor Bogani wrote:
>> 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
>>
> 
> I noticed while looking at the diff that there are more changes then
> just CONFIG_NO_HZ. Was this intentional? I thought
> CONFIG_FAIR_CGROUP_SCHED=y was the preferred setting.
> 
> rtg

Pulled. Ignore previous comment, I confused it with CONFIG_CGROUPS=y.

-- 
Tim Gardner tim.gardner at ubuntu.com