SRU Bug #229499

Tim Gardner tim.gardner at canonical.com
Tue May 13 15:40:17 UTC 2008


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
-- 
Tim Gardner tim.gardner at ubuntu.com




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