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Compiling Ubuntu 20.04 kernel with CONFIG_NO_HZ_FULL leads to multiple config errors

rated 0 times [ 2] [ 0] / answers: 1 / hits: 618 / 3 Years ago, mon, may 17, 2021, 2:21:55

I am following the steps on Build Your Own Kernel

I got a stock kernel from Ubuntu's git main

git clone git://kernel.ubuntu.com/ubuntu/ubuntu-focal.git

Then proceeded to configure the kernel

LANG=C fakeroot debian/rules clean

LANG=C fakeroot debian/rules editconfigs

Go to "General Setup/Timer Subsystem/Timer Tick Handling"

Click on "Full Dynticks System"

Go to "Preemption Model"

Select "No Forced Preemption (server)"

Repeat that for the low latency kernel and at exit I get these configuration errors

check-config: /tmp/tmp.B1SJkC9a1n/CONFIGS/amd64-config.flavour.generic: loading config

check-config: /src/ubuntu-focal/debian.master/config/annotations loading annotations

check-config: FAIL (n != y): CONFIG_NO_HZ policy<{'amd64': 'y', 'arm64': 'y', 'armhf': 

     'y', 'i386': 'y', 'ppc64el': 'y', 's390x': 'y'}>

check-config: FAIL (n != -): CONFIG_CONTEXT_TRACKING_FORCE policy<{'amd64': '-', 

       'arm64': '-', 'armhf': '-', 'i386': '-', 'ppc64el': '-', 's390x': '-'}> 

       note<LP:1349028> mark<ENFORCED>

check-config: FAIL (n != y): CONFIG_NO_HZ_IDLE policy<{'amd64': 'y', 'arm64': 'y', 

       'armhf': 'y', 'i386': 'y', 'ppc64el': 'y', 's390x': 'y'}> note<LP:1413968>

check-config: FAIL (y != n): CONFIG_NO_HZ_FULL policy<{'amd64': 'n', 'arm64': 'n', 

       'armhf': 'n', 'ppc64el': 'n'}>

check-config: FAIL (- != y): CONFIG_TICK_CPU_ACCOUNTING policy<{'amd64': 'y', 'arm64': 'y', 

       'armhf': 'y', 'i386': 'y', 'ppc64el': 'y', }>

check-config: FAIL (y != n): CONFIG_VIRT_CPU_ACCOUNTING_GEN policy<{'amd64': 'n', 

       'arm64': 'n', 'armhf': 'n', 'ppc64el': 'n'}>

If I proceed to compile the binary, it will eventually fail.

I feel like I'm going on a wild goose chase here by trying to tweak parameters manually. Is there a missing step here somewhere?

I am very confused by these check-config messages, I am not sure what they mean.

Note: I made sure I could fully compile a kernel without the modifications above. It works.

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fectlyole

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answered 3 Years ago altybol · Accepted Answer

I have never had much success using the referenced method for compiling the kernel.
The configuration change you are attempting to make has some follow on configuration dependencies and they appear to be a challenge for check-config. If I just make the one change and then let the compile process figure out the rest, I get:

doug@s19:~/kernel/linux$ scripts/diffconfig .config-6.0-rc5 .config

-TICK_CPU_ACCOUNTING y

 NO_HZ_FULL n -> y

 NO_HZ_IDLE y -> n

 VIRT_CPU_ACCOUNTING_GEN n -> y

+CONTEXT_TRACKING_USER y

+CONTEXT_TRACKING_USER_FORCE n

+RCU_NOCB_CPU y

+RCU_NOCB_CPU_DEFAULT_ALL n

+VIRT_CPU_ACCOUNTING y

Some of those you can see in your check-config list of errors.
Using this method, the kernel compiled fine for me, albeit 6.0-rc5 low latency.