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authorNick Desaulniers <ndesaulniers@google.com>2022-06-28 14:04:07 -0700
committerMasahiro Yamada <masahiroy@kernel.org>2022-07-27 21:17:59 +0900
commita6036a41bffba3d5007e377483b425d470ad8042 (patch)
tree5e2922a9b7700c8c702df80b7d6d0272996d6b1c /init
parent5439d4d4dcee548b1ad984c293225c1668045ad2 (diff)
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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/Kconfig7
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