From: Tor Vic Date: Fri, 21 Mar 2025 14:28:58 +0000 (+0100) Subject: x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel... X-Git-Tag: v6.16-rc1~191^2~2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ea1dcca1de129dfdf145338a868648bc0e24717c;p=thirdparty%2Fkernel%2Flinux.git 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 Signed-off-by: Tor Vic Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Brian Gerst Cc: Juergen Gross Cc: H. Peter Anvin Cc: Kees Cook Cc: Josh Poimboeuf Link: https://lore.kernel.org/r/20250321142859.13889-1-torvic9@mailbox.org --- diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu index 753b8763abaeb..9d108a54c30a6 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 0fc7e8fd1a2e7..436635e005e5b 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