UDS Developments

[Ralf Mardorf]

On Tue, 2012-05-08 at 14:09 -0700, Scott Lavender wrote:

>         "--" 

Please don't post under the signature lines ;).

> my understanding is that the patch is what actually changes the config
> file.  perhaps I am mistaken, however. 

It's likely that you're right, since

spinymouse at precise:~$ grep
PREEMPT /media/oz/boot/config-3.0.0-17-generic
# CONFIG_PREEMPT_RCU is not set
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set

So to set CONFIG_PREEMPT will unset PREEMPT_VOLUNTARY and might do
additional changes, e.g. it perhaps automatically will set PREEMPT_RCU.

spinymouse at precise:~$ grep FORCE /media/oz/boot/config-3.0.0-17-generic
CONFIG_IRQ_FORCED_THREADING=y

Hm, already is set.

spinymouse at precise:~$ grep HZ /media/oz/boot/config-3.0.0-17-generic
CONFIG_RCU_FAST_NO_HZ=y
CONFIG_NO_HZ=y
# CONFIG_HZ_100 is not set
CONFIG_HZ_250=y
# CONFIG_HZ_300 is not set
# CONFIG_HZ_1000 is not set
CONFIG_HZ=250
CONFIG_MACHZ_WDT=m

So the second line for a two line config patch might be to set HZ_1000.

For the same kernel source there might be a patch available that does
set two options only for the config, than running oldconfig couldn't
harm and it's ready to build the kernel.

When I build 3.0.30 I used the config of 3.2.0-23-lowlatency and only
echoed this by my build script:

# Clean LOCALVERSION
 grep CONFIG_LOCALVERSION .config
 echo "CONFIG_LOCALVERSION=\"\"" >> .config
# Optimize config
 echo "CONFIG_MK8=y" >> .config
 echo "CONFIG_DEBUG_KERNEL=n" >> .config
 echo "CONFIG_NO_HZ=n" >> .config
 make oldconfig

IIRC there was no need to clean LOCALVERSION, MK8 for optimizing to my
machine, IIRC DEBUG_KERNEL already is not set, so the echo also isn't
needed, but NO_HZ was the only option that is set. I'll check this now:

spinymouse at precise:~$ grep NO_HZ /boot/config-3.2.0-23-lowlatency
# CONFIG_NO_HZ is not set

I'm mistaken.

So when building a new kernel, there's only the need to use the config
of another lowlatency and to run oldconfig. No patch is needed, it's
only needed for the config when using the config of a generic.

- Ralf