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Message-ID: <174368720522.30396.1418171893248214427.tip-bot2@tip-bot2>
Date: Thu, 03 Apr 2025 13:33:25 -0000
From: "tip-bot2 for Tor Vic" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Tor Vic <torvic9@...lbox.org>, Ingo Molnar <mingo@...nel.org>,
Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>,
Juergen Gross <jgross@...e.com>, "H. Peter Anvin" <hpa@...or.com>,
Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/kconfig] x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU
option to locally optimize the kernel with '-march=native'
The following commit has been merged into the x86/kconfig branch of tip:
Commit-ID: ea1dcca1de129dfdf145338a868648bc0e24717c
Gitweb: https://git.kernel.org/tip/ea1dcca1de129dfdf145338a868648bc0e24717c
Author: Tor Vic <torvic9@...lbox.org>
AuthorDate: Fri, 21 Mar 2025 15:28:58 +01:00
Committer: Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 25 Mar 2025 08:24:06 +01:00
x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel with '-march=native'
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@...ux-foundation.org>
Signed-off-by: Tor Vic <torvic9@...lbox.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lore.kernel.org/r/20250321142859.13889-1-torvic9@mailbox.org
---
arch/x86/Kconfig.cpu | 14 ++++++++++++++
arch/x86/Makefile | 5 +++++
2 files changed, 19 insertions(+)
diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 753b876..9d108a5 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -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
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 0fc7e8f..436635e 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -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
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