On 04/01/25 at 17:54, Lee wrote:
On Sat, Jan 4, 2025 at 7:52 AM Franco Martelli wrote:
On 02/01/25 at 12:53, Istvan Toth wrote:
amd 5700G cpu
If you are new to kernel compiling maybe you don't know that you can
optimize the kernel for your specific CPU architecture, if you are using
the GCC compiler:
first make a backup copy of the Makefile:
$ cd linux-source-6.1
$ cp arch/x86/Makefile arch/x86/Makefile.backup
then edit "arch/x86/Makefile":
$ cd linux-source-6.1
$ vi arch/x86/Makefile
at line 152 change:
cflags-$(CONFIG_MK8) += -march=k8
to
cflags-$(CONFIG_MK8) += -march=znver3
and below at line 159 change
rustflags-$(CONFIG_MK8) += -Ctarget-cpu=k8
to
rustflags-$(CONFIG_MK8) += -Ctarget-cpu=znver3
save and exit vim. "znver3" is the GCC's switch for the µarch of your GPU.
GPU or central processing unit?
I think is a GPU, the Gentoo wiki ¹ reports that the Kernel's driver is
amdgpu ²
As long as you're not cross-compiling, how is march=znver3 better than
march=native ?
Yes, "march=native" is the better choice until you haven't trouble
(warning…) during the compile process. On my system I cannot use
"native" because the optimization option chosen by GCC (bdver2) is not
supported by objtool command, objtool is part of "linux-kbuild-6.1"
package and it doesn't support all GCC's "march" options.
So in order to compile the kernel on my system I cannot use
"march=native" but I've to use "march=bdver1". If you want to know more
please see this my old bug report ³
On my machine, 'man gcc' has the "znver1" and "znver2" strings, but no
"znver3" so it seems like "march=native" would be more correct.. or
at least less chances of an error.
... assuming there are no drawbacks to using "march=native".
To see the available options of GCC's "march" you can use this command:
$ gcc --target-help -march=foo
given a bogus architecture (foo) forces GCC to list all "march" options
in the error message.
The GCC version I use is: "gcc (Debian 12.2.0-14) 12.2.0"
¹ https://wiki.gentoo.org/wiki/Ryzen#Ryzen_7
² https://wiki.gentoo.org/wiki/AMDGPU
³ https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=935536
--
Franco Martelli
