linux-kernel - Re: [PATCH] selftests: remove obsolete kconfig fragment for cpu-hotplug

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Date:   Fri, 3 Nov 2017 15:34:31 +0800
From:   lyang0 <lei.yang@...driver.com>
To:     Sumit Semwal <sumit.semwal@...aro.org>
CC:     Shuah Khan <shuahkh@....samsung.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH] selftests: remove obsolete kconfig fragment for
 cpu-hotplug



On 2017年11月03日 11:55, Sumit Semwal wrote:
> Hello Lei,
>
> On 2 November 2017 at 07:43, lyang0 <lei.yang@...driver.com> wrote:
>>
>> On 2017年11月02日 06:59, Shuah Khan wrote:
>>> On 11/01/2017 04:52 PM, Thomas Gleixner wrote:
>>>> On Wed, 1 Nov 2017, Shuah Khan wrote:
>>>>> On 10/17/2017 08:10 PM, lei.yang@...driver.com wrote:
>>>>>> From: Lei Yang <Lei.Yang@...driver.com>
>>>>>>
>>>>>> Kconfig CONFIG_CPU_NOTIFIER_ERROR_INJECT has been removed since kernel
>>>>>> 4.10
>>>>>> check commit:
>>>>>>       commit 530e9b76ae8f863dfdef4a6ad0b38613d32e8c3f
>>>>>>       Author: Thomas Gleixner <tglx@...utronix.de>
>>>>>>       Date:   Wed Dec 21 20:19:53 2016 +0100
>>>>>>
>>>>>>           cpu/hotplug: Remove obsolete cpu hotplug register/unregister
>>>>>> functions
>>>>>>
>>>>>>           hotcpu_notifier(), cpu_notifier(), __hotcpu_notifier(),
>>>>>> __cpu_notifier(),
>>>>>>           register_hotcpu_notifier(), register_cpu_notifier(),
>>>>>>           __register_hotcpu_notifier(), __register_cpu_notifier(),
>>>>>>           unregister_hotcpu_notifier(), unregister_cpu_notifier(),
>>>>>>           __unregister_hotcpu_notifier(), __unregister_cpu_notifier()
>>>>>>        <snip>
>>>>>>
>>>>>> Signed-off-by: Lei Yang <Lei.Yang@...driver.com>
>>>>>> ---
>>>>>>    tools/testing/selftests/cpu-hotplug/config | 1 -
>>>>>>    1 file changed, 1 deletion(-)
>>>>>>
>>>>>> diff --git a/tools/testing/selftests/cpu-hotplug/config
>>>>>> b/tools/testing/selftests/cpu-hotplug/config
>>>>>> index e6ab090..d4aca2a 100644
>>>>>> --- a/tools/testing/selftests/cpu-hotplug/config
>>>>>> +++ b/tools/testing/selftests/cpu-hotplug/config
>>>>>> @@ -1,2 +1 @@
>>>>>>    CONFIG_NOTIFIER_ERROR_INJECTION=y
>>>>>> -CONFIG_CPU_NOTIFIER_ERROR_INJECT=m
>>>>>>
>>>>> Yes. It is removed from the kernel. However, selftests from the latest
>>>>> release do get run routinely on older stable releases. Dropping the
>>>>> config will impact coverage on older releases.
>>>>>
>>>>> Thomas/Greg,
>>>>>
>>>>> Any ideas on what we should do about this. On one hand it is a good idea
>>>>> to remove it, however my concern is coverage on older releases.
>>>> Can you check the kernel version on which you are running and do it
>>>> runtime
>>>> conditionally?
>>>>
>>> I have been avoiding adding kernel version checks to tests. Maybe this is
>>> one exception since the functionality is obsoleted.
>>
>>
>> I think the baseline is that we only assure kselftest  works on the release
>> it belongs to, for example, removing this config for the
>> version above 4.10, keep it in old release.  but looks it doesn't work like
>> this way.
>>
>> I think We can't  assure latest kselftest works still well on a very older
>> releases
>> yes, for some features it's common for each release. but we have some
>> features that are only available in newer
>> release.   even for the common features, it's difficult to make sure it
>> still works well for each
>> release. maintenance is a big effort if we use something like version check.
>> you never know what changes will make
>> for general feature in the future release although it's common right now.
> As Greg and several others have reiterated - the tests should be able
> to check for presence of a feature, run it if it's applicable, and
> skip if it's not. It really isn't about kernel version check, but
> writing code and test in such a way that tests can 'degrade
> gracefully', rather than fail. There are several good examples for the
> same.
>
> The idea of running newer tests is to gain coverage on older kernels
> for features still present in them, but tests weren't available at the
> time of the kernel tagging.

so we actually don't have version control for kselftest?  anytime, we 
use the latest one

I thought  we recommended use the one in 4.12 if we want to test 4.12 
kernel, not to use the one in newer version



> Hope this helps clear the doubt?

I'm wondering how do you determine this patch apply to which release.

I don't understand "Dropping the config will impact coverage on older 
releases" , we can just don't apply it to
the release older than 4.10.  then the coverage doesn't drop.

Lei



>> Lei
>>
>>
>>> In any case, just removing the config isn't the complete solution. I will
>>> have to think about this some.
>>>
>>> thanks,
>>> -- Shuah
>>>
>>> --
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>>
> Best,
> Sumit.
> --
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