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x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel with '-march=native'

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Add a 'native' option that allows users to build an optimized kernel for
their local machine (i.e. the machine which is used to build the kernel)
by passing '-march=native' to CFLAGS.

The idea comes from Linus' reply to Arnd's initial proposal:

  https://lore.kernel.org/all/CAHk-=wji1sV93yKbc==Z7OSSHBiDE=LAdG_d5Y-zPBrnSs0k2A@mail.gmail.com/

Here are some numbers comparing 'generic' to 'native' on a Skylake dual-core
laptop (generic --> native):

  - vmlinux and compressed modules size:
      125'907'744 bytes --> 125'595'280 bytes  (-0.248 %)
      18'810 kilobytes --> 18'770 kilobytes    (-0.213 %)

  - phoronix, average of 3 runs:
      ffmpeg:
      130.99 --> 131.15                        (+0.122 %)
      nginx:
      10'650 --> 10'725                        (+0.704 %)
      hackbench (lower is better):
      102.27 --> 99.50                         (-2.709 %)

  - xz compression of firefox tarball (lower is better):
      319.57 seconds --> 317.34 seconds        (-0.698 %)

  - stress-ng, bogoops, average of 3 15-second runs:
      fork:
      111'744 --> 115'509                      (+3.397 %)
      bsearch:
      7'211 --> 7'436                          (+3.120 %)
      memfd:
      3'591 --> 3'604                          (+0.362 %)
      mmapfork:
      630 --> 629                              (-0.159 %)
      schedmix:
      42'715 --> 43'251                        (+1.255 %)
      epoll:
      2'443'767 --> 2'454'413                  (+0.436 %)
      vm:
      1'442'256 --> 1'486'615                  (+3.076 %)

  - schbench (two message threads), 30-second runs:
      304 rps --> 305 rps                      (+0.329 %)

There is little difference both in terms of size and of performance, however
the native build comes out on top ever so slightly.

[ mingo: Renamed the option to CONFIG_X86_NATIVE_CPU, expanded the help text
         and added Linus's Suggested-by tag. ]

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Tor Vic <torvic9@mailbox.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250321142859.13889-1-torvic9@mailbox.org
This commit is contained in:
Tor Vic
2025-03-21 15:28:58 +01:00
committed by Ingo Molnar
parent 2df0c02dab
commit ea1dcca1de
2 changed files with 19 additions and 0 deletions
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14
arch/x86/Kconfig.cpu
View File

@@ -245,6 +245,20 @@ config MATOM
endchoice
config X86_NATIVE_CPU
bool "Build and optimize for local/native CPU"
depends on X86_64
default n
help
Optimize for the current CPU used to compile the kernel.
Use this option if you intend to build the kernel for your
local machine.
Note that such a kernel might not work optimally on a
different x86 machine.
If unsure, say N.
config X86_GENERIC
bool "Generic x86 support"
depends on X86_32

5
arch/x86/Makefile
View File

@@ -173,8 +173,13 @@ else
# Use -mskip-rax-setup if supported.
KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)
ifdef CONFIG_X86_NATIVE_CPU
KBUILD_CFLAGS += -march=native
KBUILD_RUSTFLAGS += -Ctarget-cpu=native
else
KBUILD_CFLAGS += -march=x86-64 -mtune=generic
KBUILD_RUSTFLAGS += -Ctarget-cpu=x86-64 -Ztune-cpu=generic
endif
KBUILD_CFLAGS += -mno-red-zone
KBUILD_CFLAGS += -mcmodel=kernel