Re: 2.7% build time regression caused by enabling debug/printk.scc KERNEL_FEATURE]

["Aníbal Limón" <anibal.limon@linux.intel.com>]

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On 07/27/2016 03:06 PM, Sullivan, California L wrote:
> Adding the debug-kernel fragment to the printk fragment was probably a
> mistake on my part. I don't see anything that requires it.
> 
> I'm also seeing another issue: TTY_PRINTK depends on EXPERT, which is
> only enabled on the developer kernel by default, so you currently won't
> be getting that option. From there, if we were to enable EXPERT,
> DEBUG_KERNEL then gets selected automatically and we essentially end up
> where we started and have the build time regression.
> 
> Stuff to think about on my end I suppose. In the mean time I +1 removing
> the debug-kernel include from printk.scc.

I agree,

	alimon

> 
> ---
> Cal
> 
> On 07/27/2016 07:31 AM, Bruce Ashfield wrote:
>> On 2016-07-27 09:18 AM, Ed Bartosh wrote:
>>> On Wed, Jul 27, 2016 at 09:06:44AM -0400, Bruce Ashfield wrote:
>>>> On 2016-07-27 08:28 AM, Ed Bartosh wrote:
>>>>> Hi Bruce,
>>>>>
>>>>> Thank you for your suggestion to experiment with configuration options!
>>>>>
>>>>>> On 2016-07-26 10:32 AM, Ed Bartosh wrote:
>>>>>>> Hi all,
>>>>>>>
>>>>>>> We've noticed quite big increase of core-image-minimal build time caused by commit
>>>>>>> d55b7650d305ffad953dd36595ee6b9aa8df5a72 linux-yocto: Enablei debug/printk.scc KERNEL_FEATURE on qemuall machines.
>>>>>>>
>>>>>> That commit only enables the following options:
>>>>>>
>>>>>> CONFIG_PRINTK=y
>>>>>> CONFIG_PRINTK_TIME=y
>>>>>>
>>>>>> CONFIG_EARLY_PRINTK=y
>>>>>>
>>>>>> CONFIG_EARLY_PRINTK_DBGP=y
>>>>>> CONFIG_EARLY_PRINTK_EFI=y
>>>>>> CONFIG_TTY_PRINTK=y
>>>>>>
>>>>>> And yes, that will add some size to the kernel, but I'm not seeing
>>>>>> similar size increases here.
>>>>>>
>>>>>> If you take a look through the kernel source and build, there are
>>>>>> relatively few additions to the actual kernel build that change
>>>>>> based on those options, and most of them are runtime changes versus
>>>>>> build-time changes.
>>>>>>
>>>>> The actuall difference in configuration is bigger as far as I can see:
>>>>> $ diff -u ../build-kernel/tmp/work/qemux86_64-poky-linux/linux-yocto/4.4.14+gitAUTOINC+4800a400d5_8361321fec-r0/image/boot/config-4.4.14-yocto-standard
>>>>> tmp/work/qemux86_64-poky-linux/linux-yocto/4.4.14+gitAUTOINC+4800a400d5_8361321fec-r0/image/boot/config-4.4.14-yocto-standard | grep '^+C'
>>>>> +CONFIG_CONSOLE_POLL=y
>>>>> +CONFIG_PRINTK_TIME=y
>>>>> +CONFIG_DEBUG_INFO=y
>>>>> +CONFIG_DEBUG_KERNEL=y
>>>>> +CONFIG_SCHED_DEBUG=y
>>>>> +CONFIG_DEBUG_PREEMPT=y
>>>>> +CONFIG_KGDB=y
>>>>> +CONFIG_KGDB_SERIAL_CONSOLE=y
>>>>> +CONFIG_KGDB_LOW_LEVEL_TRAP=y
>>>>> +CONFIG_KGDB_KDB=y
>>>>> +CONFIG_KDB_DEFAULT_ENABLE=0x1
>>>>> +CONFIG_KDB_KEYBOARD=y
>>>>> +CONFIG_KDB_CONTINUE_CATASTROPHIC=0
>>>>> +CONFIG_EARLY_PRINTK_DBGP=y
>>>>> +CONFIG_EARLY_PRINTK_EFI=y
>>>>> +CONFIG_DEBUG_RODATA=y
>>>>> +CONFIG_DEBUG_RODATA_TEST=y
>>>>> +CONFIG_X86_DEBUG_FPU=y
>>>>>
>>>>> I guess the reason of this is that printk.scc includes debug-kernel.scc,
>>>>> which brings more config options:
>>>>> CONFIG_DEBUG_KERNEL=y
>>>>> CONFIG_DEBUG_INFO=y
>>>>> CONFIG_DEBUG_PREEMPT=y
>>>>>
>>>>> That probably explains the difference in kernel size and compile time.
>>>>>
>>>> Yup.
>>>>
>>>>> After removing 'include debug-kernel.scc' the difference in
>>>>> configuration became more reasonable:
>>>>> +CONFIG_PRINTK_TIME=y
>>>>> +CONFIG_EARLY_PRINTK_DBGP=y
>>>>> +CONFIG_EARLY_PRINTK_EFI=y
>>>>>
>>>>> And the size of kernel and modules became almost the same as before
>>>>> enabling printk feature.
>>>>>
>>>>> Considering that the rest of the options from printk.scc don't appear in
>>>>> the result configuration even if debug-kernel.scc is included I hope
>>>>> it should be ok to remove 'include debug-kernel.scc' from printk.scc.
>>>>>
>>>>> Does it make sense for you?
>>>> It does to me. Since we actually have a "developer" kernel type that
>>>> is intended for this purpose. Anything that we add to the standard
>>>> kernel type should be more surgical.
>>>>
>>> Looking at guilty commit
>>> https://git.yoctoproject.org/cgit/cgit.cgi/yocto-kernel-cache/commit/?h=yocto-4.4&id=fd8d90ca69f53d425fdb34fc9a9debac1d0c5f52
>>> I'd say that the rest of scc files should be also tested the same way.
>>> We may not need to enable all 3 CONFIG_DEBUG options for each of them.
>> Adding Cal, since he did the work on this split up.
>>
>> The profiling feature makes sense with debug kernel being included, but
>> I can see some latency top use cases that would be valid with a non
>> developer mode kernel (i.e. the standard kernel).
>>
>> But yes, we don't want fragments that could be included by the standard
>> kernel to add typical functionality to add more than they need to
>> function. Further tweaking can be done, its part of the iterative
>> process on these fragments as we work through use cases.
>>
>> Bruce
>>
>>>
>>> --
>>> Regards,
>>> Ed
>>>
>>
> 


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