[LEDE-DEV] [PATCH] config: add option to select kernel compile optimization type

[Jonas Gorski]

On 22 January 2018 at 10:20, Koen Vandeputte
<koen.vandeputte at ncentric.com> wrote:
>
>
> On 2018-01-21 13:37, Jonas Gorski wrote:
>>
>> Hi,
>>
>> On 18 January 2018 at 10:50, Koen Vandeputte
>> <koen.vandeputte at ncentric.com> wrote:
>>>
>>> A lot of targets have more than sufficient space to allow
>>> building the kernel for speed iso size.
>>>
>>> Export this performance option to the main config:
>>>
>>> - Making it easy accessable for users
>>> - Discarding the need to adjust it in the kernel config each time
>>> when building from scratch and only using "make oldconfig"
>>>
>>> Compiling for size is still the default.
>>
>> This would be a "regression" for layerscape, as this target sets
>> CC_OPTIMIZE_FOR_PERFORMANCE to y.
>>
>>> Purely informational:
>>>
>>> On my cns3xxx board, kernel size increases by ~100kB
>>> but boot time decreased by ~8%.
>>>
>>> Signed-off-by: Koen Vandeputte <koen.vandeputte at ncentric.com>
>>> ---
>>>   config/Config-kernel.in | 16 ++++++++++++++++
>>>   1 file changed, 16 insertions(+)
>>>
>>> diff --git a/config/Config-kernel.in b/config/Config-kernel.in
>>> index fa06b5044219..b98c5dd04591 100644
>>> --- a/config/Config-kernel.in
>>> +++ b/config/Config-kernel.in
>>> @@ -194,6 +194,22 @@ config KERNEL_DEBUG_GPIO
>>>          bool "Compile the kernel with gpio debugging"
>>>          select KERNEL_DEBUG_KERNEL
>>>
>>> +config KERNEL_CC_OPTIMIZE_FOR_PERFORMANCE
>>> +        bool
>>> +        default y if COMPILE_KERNEL_FOR_SPEED
>>> +        default n
>>> +
>>> +config KERNEL_CC_OPTIMIZE_FOR_SIZE
>>> +        bool
>>> +        default n if COMPILE_KERNEL_FOR_SPEED
>>> +        default y
>>> +
>>> +config COMPILE_KERNEL_FOR_SPEED
>>> +        bool "Optimize the kernel for speed instead of size"
>>> +        default n
>>> +        help
>>> +          This will compile your kernel for maximum speed (-O2) instead
>>> of smaller size (-Os)
>>
>> The kernel uses a choice here, so I think it would be better to just
>> copy that. One less config option as well.
>
> Hi Jonas,
>
> Could you elaborate a bit more on this specific point?
> I'm not quite fully understanding your proposal here.

See http://elixir.free-electrons.com/linux/latest/source/init/Kconfig#L1034


Regards
Jonas