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Build native kernel with DEBUG_FORCE_FUNCTION_ALIGN_32B #2332

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insilications opened this issue Apr 16, 2021 · 1 comment
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Build native kernel with DEBUG_FORCE_FUNCTION_ALIGN_32B #2332

insilications opened this issue Apr 16, 2021 · 1 comment
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@miguelinux
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@insilications
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There are cases that a commit from one domain changes the function address alignment of other domains, and cause magic performance bump (regression or improvement). 
Enable this option will help to verify if the bump is caused by function alignment changes, while it will slightly increase the kernel size and affect icache usage.

It is mainly for debug and performance tuning use.

https://github.com/torvalds/linux/blob/v5.10/Makefile#L900:

ifdef CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_32B
KBUILD_CFLAGS += -falign-functions=32
endif

En passant: 5.12 will be released with official Clang LTO support (LLVM 12 has been released). There are also some patches for using GCC LTO, for those who want it (https://github.com/andikleen/linux-misc/tree/lto-5.11-2).
https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.12-Clang-LTO-Merged
@insilications
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@miguelinux can you take a look into this to see if it is worth it? Please? ❤️

@miguelinux miguelinux self-assigned this Jun 3, 2021
clrpackages pushed a commit to clearlinux-pkgs/linux that referenced this issue Jul 29, 2021
@miguelinux @clrpackages
config: set DEBUG_FORCE_FUNCTION_ALIGN_32B
719ccc0 
There are cases that a commit from one domain changes the function
address alignment of other domains, and cause magic performance bump
(regression or improvement).
Enable this option will help to verify if the bump is caused by function
alignment changes, while it will slightly increase the kernel size and
affect icache usage.

It is mainly for debug and performance tuning use.

resolves clearlinux/distribution#2332
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@miguelinux miguelinux

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@miguelinux @insilications