Re: [PATCH] compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING

Heiko Carstens
2019-03-21T08:01:46Z

On Wed, Mar 20, 2019 at 03:20:27PM +0900, Masahiro Yamada wrote:
> Commit 60a3cdd06394 ("x86: add optimized inlining") introduced
> CONFIG_OPTIMIZE_INLINING, but it has been available only for x86.
>
> The idea is obviously arch-agnostic although we need some code fixups.
> This commit moves the config entry from arch/x86/Kconfig.debug to
> lib/Kconfig.debug so that all architectures (except MIPS for now) can
> benefit from it.
>
> At this moment, I added "depends on !MIPS" because fixing 0day bot reports
> for MIPS was complex to me.
>
> I tested this patch on my arm/arm64 boards.
>
> This can make a huge difference in kernel image size especially when
> CONFIG_OPTIMIZE_FOR_SIZE is enabled.
>
> For example, I got 3.5% smaller arm64 kernel image for v5.1-rc1.
>
> dec file
> 18983424 arch/arm64/boot/Image.before
> 18321920 arch/arm64/boot/Image.after

Well, this will change, since now people (have to) start adding
__always_inline annotations on all architectures, most likely until
all have about the same amount of annotations like x86. This will
reduce the benefit.

Not sure if it's really a win that we get the inline vs
__always_inline discussion now on all architectures.