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| author | Nick Desaulniers <ndesaulniers@google.com> | 2022-06-28 14:04:07 -0700 |
|---|---|---|
| committer | Masahiro Yamada <masahiroy@kernel.org> | 2022-07-27 21:17:59 +0900 |
| commit | a6036a41bffba3d5007e377483b425d470ad8042 (patch) | |
| tree | 5e2922a9b7700c8c702df80b7d6d0272996d6b1c /init | |
| parent | 5439d4d4dcee548b1ad984c293225c1668045ad2 (diff) | |
| download | linux-stable-a6036a41bffba3d5007e377483b425d470ad8042.tar.gz linux-stable-a6036a41bffba3d5007e377483b425d470ad8042.tar.bz2 linux-stable-a6036a41bffba3d5007e377483b425d470ad8042.zip | |
kbuild: drop support for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3
The difference in most compilers between `-O3` and `-O2` is mostly down
to whether loops with statically determinable trip counts are fully
unrolled vs unrolled to a multiple of SIMD width.
This patch is effectively a revert of
commit 15f5db60a137 ("kbuild,arc: add
CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 for ARC") without re-adding
ARCH_CFLAGS
Ever since
commit cfdbc2e16e65 ("ARC: Build system: Makefiles, Kconfig, Linker
script")
ARC has been built with -O3, though the reason for doing so was not
specified in inline comments or the commit message. This commit does not
re-add -O3 to arch/arc/Makefile.
Folks looking to experiment with `-O3` (or any compiler flag for that
matter) may pass them along to the command line invocation of make:
$ make KCFLAGS=-O3
Code that looks to re-add an explicit Kconfig option for `-O3` should
provide:
1. A rigorous and reproducible performance profile of a reasonable
userspace workload that demonstrates a hot loop in the kernel that
would benefit from `-O3` over `-O2`.
2. Disassembly of said loop body before and after.
3. Provides stats on terms of increase in file size.
Link: https://lore.kernel.org/linux-kbuild/CA+55aFz2sNBbZyg-_i8_Ldr2e8o9dfvdSfHHuRzVtP2VMAUWPg@mail.gmail.com/
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Diffstat (limited to 'init')
| -rw-r--r-- | init/Kconfig | 7 |
1 files changed, 0 insertions, 7 deletions
diff --git a/init/Kconfig b/init/Kconfig index c7900e8975f1..1b4d8acc3def 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1401,13 +1401,6 @@ config CC_OPTIMIZE_FOR_PERFORMANCE with the "-O2" compiler flag for best performance and most helpful compile-time warnings. -config CC_OPTIMIZE_FOR_PERFORMANCE_O3 - bool "Optimize more for performance (-O3)" - depends on ARC - help - Choosing this option will pass "-O3" to your compiler to optimize - the kernel yet more for performance. - config CC_OPTIMIZE_FOR_SIZE bool "Optimize for size (-Os)" help |