[PATCH] x86/cpu: Add support for modern x86-64-v* march

[Dimitri John Ledkov]

Add support for setting march to x86-64-v2, x86-64-v3, x86-64-v4 with
tuning set to an early family of CPUs that support such instruction
levels. By default gcc sets generic tuning for x86-64-v*, which is
suboptimal for all brands of CPUs with such instruction set support.

Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@xxxxxxxxxxxxx>
---
 arch/x86/Kconfig.cpu | 23 ++++++++++++++++++++++-
 arch/x86/Makefile    | 11 +++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 00468adf18..70e70b4733 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -294,6 +294,27 @@ config GENERIC_CPU
 	  Generic x86-64 CPU.
 	  Run equally well on all x86-64 CPUs.
 
+config X86_64_V2
+	bool "x86-64-v2"
+	depends on X86_64
+	help
+	  x86-64-v2 CPU.
+	  Run well on x86-64-v2 capable CPUs.
+
+config X86_64_V3
+	bool "x86-64-v3"
+	depends on X86_64
+	help
+	  x86-64-v3 CPU.
+	  Run well on x86-64-v3 capable CPUs.
+
+config X86_64_V4
+	bool "x86-64-v4"
+	depends on X86_64
+	help
+	  x86-64-v4 CPU.
+	  Run well on x86-64-v4 capable CPUs.
+
 endchoice
 
 config X86_GENERIC
@@ -318,7 +339,7 @@ config X86_INTERNODE_CACHE_SHIFT
 config X86_L1_CACHE_SHIFT
 	int
 	default "7" if MPENTIUM4 || MPSC
-	default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU
+	default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU || X86_64_V2 || X86_64_V3 || X86_64_V4
 	default "4" if MELAN || M486SX || M486 || MGEODEGX1
 	default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
 
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index fdc2e3abd6..ee97501970 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -154,6 +154,14 @@ else
         cflags-$(CONFIG_MCORE2)		+= -march=core2
         cflags-$(CONFIG_MATOM)		+= -march=atom
         cflags-$(CONFIG_GENERIC_CPU)	+= -mtune=generic
+        # Note gcc for -march=x86-64-v* sets genetic tuning only,
+        # rather than something sensible / minimum tuning from the
+        # same family. Set mtune to early family of CPUs that support
+        # such instructions, which works better across all CPU brands.
+        cflags-$(CONFIG_X86_64_V2)	+= -march=x86-64-v2 -mtune=nehalem
+        cflags-$(CONFIG_X86_64_V3)	+= -march=x86-64-v3 -mtune=skylake
+        cflags-$(CONFIG_X86_64_V4)	+= -march=x86-64-v4 -mtune=skylake-avx512
+
         KBUILD_CFLAGS += $(cflags-y)
 
         rustflags-$(CONFIG_MK8)		+= -Ctarget-cpu=k8
@@ -161,6 +169,9 @@ else
         rustflags-$(CONFIG_MCORE2)	+= -Ctarget-cpu=core2
         rustflags-$(CONFIG_MATOM)	+= -Ctarget-cpu=atom
         rustflags-$(CONFIG_GENERIC_CPU)	+= -Ztune-cpu=generic
+        rustflags-$(CONFIG_X86_64_V2)	+= -Ctarget-cpu=x86-64-v2
+        rustflags-$(CONFIG_X86_64_V3)	+= -Ctarget-cpu=x86-64-v3
+        rustflags-$(CONFIG_X86_64_V4)	+= -Ctarget-cpu=x86-64-v4
         KBUILD_RUSTFLAGS += $(rustflags-y)
 
         KBUILD_CFLAGS += -mno-red-zone
-- 
2.34.1