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Message-ID: <20250321142859.13889-1-torvic9@mailbox.org>
Date: Fri, 21 Mar 2025 15:28:58 +0100
From: Tor Vic <torvic9@...lbox.org>
To: arnd@...nel.org,
x86@...nel.org,
linux-kernel@...r.kernel.org
Cc: bp@...en8.de,
tglx@...utronix.de,
mingo@...hat.com,
hpa@...or.com
Subject: [PATCH] arch/x86: Add an option to build the kernel with '-march=native' on x86-64
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 the CFLAGS.
The idea comes from Linus' reply to Arnd's initial proposal in [1].
This patch is based on Arnd's x86 cleanup series, which is now in -tip [2].
[1] https://lore.kernel.org/all/CAHk-=wji1sV93yKbc==Z7OSSHBiDE=LAdG_d5Y-zPBrnSs0k2A@mail.gmail.com/
[2] https://lore.kernel.org/all/20250226213714.4040853-1-arnd@kernel.org/
Signed-off-by: Tor Vic <torvic9@...lbox.org>
---
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.
---
arch/x86/Kconfig.cpu | 9 +++++++++
arch/x86/Makefile | 5 +++++
2 files changed, 14 insertions(+)
diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 8fcb8ccee44b..057d7c28b794 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -245,6 +245,15 @@ config MATOM
endchoice
+config NATIVE_CPU
+ bool "Build for 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.
+
config X86_GENERIC
bool "Generic x86 support"
depends on X86_32
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 8120085b00a4..0075bace3ed9 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -178,8 +178,13 @@ else
# Use -mskip-rax-setup if supported.
KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)
+ifdef CONFIG_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
--
2.49.0
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