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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] [RFC] x86/cpu: rework instruction set selection
On April 25, 2025 7:15:15 AM PDT, Arnd Bergmann <arnd@xxxxxxxxxx> wrote: >From: Arnd Bergmann <arnd@xxxxxxxx> > >With cx8 and tsc being mandatory features, the only important >architectural features are now cmov and pae. > >Change the large list of target CPUs to no longer pick the instruction set >itself but only the mtune= optimization level and in-kernel optimizations >that remain compatible with all cores. > >The CONFIG_X86_CMOV instead becomes user-selectable and is now how >Kconfig picks between 586-class (Pentium, Pentium MMX, K6, C3, GeodeGX) >and 686-class (everything else) targets. > >In order to allow running on late 32-bit cores (Athlon, Pentium-M, >Pentium 4, ...), the X86_L1_CACHE_SHIFT can no longer be set to anything >lower than 6 (i.e. 64 byte cache lines). > >The optimization options now depend on X86_CMOV and X86_PAE instead >of the other way round, while other compile-time conditionals that >checked for MATOM/MGEODEGX1 instead now check for CPU_SUP_* options >that enable support for a particular CPU family. > >Link: >https://lore.kernel.org/lkml/dd29df0c-0b4f-44e6-b71b-2a358ea76fb4@xxxxxxxxxxxxxxxx/ >Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> >--- >This is what I had in mind as mentioned in the earlier thread on >cx8/tsc removal. I based this on top of the Ingo's [RFC 15/15] >patch. >--- > arch/x86/Kconfig | 2 +- > arch/x86/Kconfig.cpu | 100 ++++++++++++++------------------ > arch/x86/Makefile_32.cpu | 48 +++++++-------- > arch/x86/include/asm/vermagic.h | 36 +----------- > arch/x86/kernel/tsc.c | 2 +- > arch/x86/xen/Kconfig | 1 - > drivers/misc/mei/Kconfig | 2 +- > 7 files changed, 74 insertions(+), 117 deletions(-) > >diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >index a9d717558972..1e33f88c9b97 100644 >--- a/arch/x86/Kconfig >+++ b/arch/x86/Kconfig >@@ -1438,7 +1438,7 @@ config HIGHMEM > > config X86_PAE > bool "PAE (Physical Address Extension) Support" >- depends on X86_32 && X86_HAVE_PAE >+ depends on X86_32 && X86_CMOV > select PHYS_ADDR_T_64BIT > help > PAE is required for NX support, and furthermore enables >diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu >index 6f1e8cc8fe58..0619566de93f 100644 >--- a/arch/x86/Kconfig.cpu >+++ b/arch/x86/Kconfig.cpu >@@ -1,23 +1,32 @@ > # SPDX-License-Identifier: GPL-2.0 > # Put here option for CPU selection and depending optimization >-choice >- prompt "x86-32 Processor family" >- depends on X86_32 >- default M686 >+ >+config X86_CMOV >+ bool "Require 686-class CMOV instructions" if X86_32 >+ default y > help >- This is the processor type of your CPU. This information is >- used for optimizing purposes. In order to compile a kernel >- that can run on all supported x86 CPU types (albeit not >- optimally fast), you can specify "586" here. >+ Most x86-32 processor implementations are compatible with >+ the the CMOV instruction originally added in the Pentium Pro, >+ and they perform much better when using it. >+ >+ Disable this option to build for 586-class CPUs without this >+ instruction. This is only required for the original Intel >+ Pentium (P5, P54, P55), AMD K6/K6-II/K6-3D, Geode GX1 and Via >+ CyrixIII/C3 CPUs. > > Note that the 386 and 486 is no longer supported, this includes > AMD/Cyrix/Intel 386DX/DXL/SL/SLC/SX, Cyrix/TI 486DLC/DLC2, > UMC 486SX-S and the NexGen Nx586, AMD ELAN and all 486 based > CPUs. > >- The kernel will not necessarily run on earlier architectures than >- the one you have chosen, e.g. a Pentium optimized kernel will run on >- a PPro, but not necessarily on a i486. >+choice >+ prompt "x86-32 Processor optimization" >+ depends on X86_32 >+ default X86_GENERIC >+ help >+ This is the processor type of your CPU. This information is >+ used for optimizing purposes, but does not change compatibility >+ with other CPU types. > > Here are the settings recommended for greatest speed: > - "586" for generic Pentium CPUs lacking the TSC >@@ -45,14 +54,13 @@ choice > > config M586TSC > bool "Pentium-Classic" >- depends on X86_32 >+ depends on X86_32 && !X86_CMOV > help >- Select this for a Pentium Classic processor with the RDTSC (Read >- Time Stamp Counter) instruction for benchmarking. >+ Select this for a Pentium Classic processor. > > config M586MMX > bool "Pentium-MMX" >- depends on X86_32 >+ depends on X86_32 && !X86_CMOV > help > Select this for a Pentium with the MMX graphics/multimedia > extended instructions. >@@ -117,7 +125,7 @@ config MPENTIUM4 > > config MK6 > bool "K6/K6-II/K6-III" >- depends on X86_32 >+ depends on X86_32 && !X86_CMOV > help > Select this for an AMD K6-family processor. Enables use of > some extended instructions, and passes appropriate optimization >@@ -125,7 +133,7 @@ config MK6 > > config MK7 > bool "Athlon/Duron/K7" >- depends on X86_32 >+ depends on X86_32 && !X86_PAE > help > Select this for an AMD Athlon K7-family processor. Enables use of > some extended instructions, and passes appropriate optimization >@@ -147,42 +155,37 @@ config MEFFICEON > > config MGEODEGX1 > bool "GeodeGX1" >- depends on X86_32 >+ depends on X86_32 && !X86_CMOV > help > Select this for a Geode GX1 (Cyrix MediaGX) chip. > > config MGEODE_LX > bool "Geode GX/LX" >- depends on X86_32 >+ depends on X86_32 && !X86_PAE > help > Select this for AMD Geode GX and LX processors. > > config MCYRIXIII > bool "CyrixIII/VIA-C3" >- depends on X86_32 >+ depends on X86_32 && !X86_CMOV > help > Select this for a Cyrix III or C3 chip. Presently Linux and GCC > treat this chip as a generic 586. Whilst the CPU is 686 class, > it lacks the cmov extension which gcc assumes is present when > generating 686 code. >- Note that Nehemiah (Model 9) and above will not boot with this >- kernel due to them lacking the 3DNow! instructions used in earlier >- incarnations of the CPU. > > config MVIAC3_2 > bool "VIA C3-2 (Nehemiah)" >- depends on X86_32 >+ depends on X86_32 && !X86_PAE > help > Select this for a VIA C3 "Nehemiah". Selecting this enables usage > of SSE and tells gcc to treat the CPU as a 686. >- Note, this kernel will not boot on older (pre model 9) C3s. > > config MVIAC7 > bool "VIA C7" >- depends on X86_32 >+ depends on X86_32 && !X86_PAE > help >- Select this for a VIA C7. Selecting this uses the correct cache >- shift and tells gcc to treat the CPU as a 686. >+ Select this for a VIA C7. > > config MATOM > bool "Intel Atom" >@@ -192,20 +195,19 @@ config MATOM > accordingly optimized code. Use a recent GCC with specific Atom > support in order to fully benefit from selecting this option. > >-endchoice >- > config X86_GENERIC >- bool "Generic x86 support" >- depends on X86_32 >+ bool "Generic x86" > help >- Instead of just including optimizations for the selected >+ Instead of just including optimizations for a particular > x86 variant (e.g. PII, Crusoe or Athlon), include some more > generic optimizations as well. This will make the kernel >- perform better on x86 CPUs other than that selected. >+ perform better on a variety of CPUs. > > This is really intended for distributors who need more > generic optimizations. > >+endchoice >+ > # > # Define implied options from the CPU selection here > config X86_INTERNODE_CACHE_SHIFT >@@ -216,17 +218,14 @@ config X86_INTERNODE_CACHE_SHIFT > config X86_L1_CACHE_SHIFT > int > default "7" if MPENTIUM4 >- default "6" if MK7 || MPENTIUMM || MATOM || MVIAC7 || X86_GENERIC || >X86_64 >- default "4" if MGEODEGX1 >- default "5" if MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII >|| MPENTIUMII || M686 || M586MMX || M586TSC || MVIAC3_2 || MGEODE_LX >+ default "6" > > config X86_F00F_BUG >- def_bool y >- depends on M586MMX || M586TSC || M586 >+ def_bool !X86_CMOV > > config X86_ALIGNMENT_16 > def_bool y >- depends on MCYRIXIII || MK6 || M586MMX || M586TSC || M586 || MVIAC3_2 >|| MGEODEGX1 >+ depends on MCYRIXIII || MK6 || M586MMX || M586TSC || M586 || MVIAC3_2 >|| MGEODEGX1 || (!X86_CMOV && X86_GENERIC) > > config X86_INTEL_USERCOPY > def_bool y >@@ -234,34 +233,23 @@ config X86_INTEL_USERCOPY > > config X86_USE_PPRO_CHECKSUM > def_bool y >- depends on MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || >MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MEFFICEON || >MGEODE_LX || MATOM >+ depends on MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || >MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MEFFICEON || >MGEODE_LX || MATOM || (X86_CMOV && X86_GENERIC) > > config X86_TSC > def_bool y > >-config X86_HAVE_PAE >- def_bool y >- depends on MCRUSOE || MEFFICEON || MCYRIXIII || MPENTIUM4 || MPENTIUMM >|| MPENTIUMIII || MPENTIUMII || M686 || MVIAC7 || MATOM || X86_64 >- > config X86_CX8 > def_bool y > >-# this should be set for all -march=.. options where the compiler >-# generates cmov. >-config X86_CMOV >- def_bool y >- depends on (MK7 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII >|| M686 || MVIAC3_2 || MVIAC7 || MCRUSOE || MEFFICEON || MATOM || MGEODE_LX || >X86_64) >- > config X86_MINIMUM_CPU_FAMILY > int > default "64" if X86_64 >- default "6" if X86_32 && (MPENTIUM4 || MPENTIUMM || MPENTIUMIII || >MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MEFFICEON || MATOM || MK7) >- default "5" if X86_32 >- default "4" >+ default "6" if X86_32 && X86_CMOV >+ default "5" > > config X86_DEBUGCTLMSR > def_bool y >- depends on !(MK6 || MCYRIXIII || M586MMX || M586TSC || M586) && !UML >+ depends on X86_CMOV && !UML > > config IA32_FEAT_CTL > def_bool y >@@ -297,7 +285,7 @@ config CPU_SUP_INTEL > config CPU_SUP_CYRIX_32 > default y > bool "Support Cyrix processors" if PROCESSOR_SELECT >- depends on M586 || M586TSC || M586MMX || (EXPERT && !64BIT) >+ depends on !64BIT > help > This enables detection, tunings and quirks for Cyrix processors > >diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu >index f5e933077bf4..ebd7ec6eaf34 100644 >--- a/arch/x86/Makefile_32.cpu >+++ b/arch/x86/Makefile_32.cpu >@@ -10,30 +10,32 @@ else > align := -falign-functions=0 -falign-jumps=0 -falign-loops=0 > endif > >-cflags-$(CONFIG_M586TSC) += -march=i586 >-cflags-$(CONFIG_M586MMX) += -march=pentium-mmx >-cflags-$(CONFIG_M686) += -march=i686 >-cflags-$(CONFIG_MPENTIUMII) += -march=i686 $(call tune,pentium2) >-cflags-$(CONFIG_MPENTIUMIII) += -march=i686 $(call tune,pentium3) >-cflags-$(CONFIG_MPENTIUMM) += -march=i686 $(call tune,pentium3) >-cflags-$(CONFIG_MPENTIUM4) += -march=i686 $(call tune,pentium4) >-cflags-$(CONFIG_MK6) += -march=k6 >-# Please note, that patches that add -march=athlon-xp and friends are >pointless. >-# They make zero difference whatsosever to performance at this time. >-cflags-$(CONFIG_MK7) += -march=athlon >-cflags-$(CONFIG_MCRUSOE) += -march=i686 $(align) >-cflags-$(CONFIG_MEFFICEON) += -march=i686 $(call tune,pentium3) $(align) >-cflags-$(CONFIG_MCYRIXIII) += $(call cc-option,-march=c3,-march=i486) >$(align) >-cflags-$(CONFIG_MVIAC3_2) += $(call cc-option,-march=c3-2,-march=i686) >-cflags-$(CONFIG_MVIAC7) += -march=i686 >-cflags-$(CONFIG_MATOM) += -march=atom >+ifdef CONFIG_X86_CMOV >+cflags-y += -march=i686 >+else >+cflags-y += -march=i586 >+endif > >-# Geode GX1 support >-cflags-$(CONFIG_MGEODEGX1) += -march=pentium-mmx >-cflags-$(CONFIG_MGEODE_LX) += $(call >cc-option,-march=geode,-march=pentium-mmx) >-# add at the end to overwrite eventual tuning options from earlier >-# cpu entries >-cflags-$(CONFIG_X86_GENERIC) += $(call tune,generic,$(call tune,i686)) >+cflags-$(CONFIG_M586TSC) += -mtune=i586 >+cflags-$(CONFIG_M586MMX) += -mtune=pentium-mmx >+cflags-$(CONFIG_M686) += -mtune=i686 >+cflags-$(CONFIG_MPENTIUMII) += -mtune=pentium2 >+cflags-$(CONFIG_MPENTIUMIII) += -mtune=pentium3 >+cflags-$(CONFIG_MPENTIUMM) += -mtune=pentium3 >+cflags-$(CONFIG_MPENTIUM4) += -mtune=pentium4 >+cflags-$(CONFIG_MK6) += -mtune=k6 >+# Please note, that patches that add -mtune=athlon-xp and friends are >pointless. >+# They make zero difference whatsosever to performance at this time. >+cflags-$(CONFIG_MK7) += -mtune=athlon >+cflags-$(CONFIG_MCRUSOE) += -mtune=i686 $(align) >+cflags-$(CONFIG_MEFFICEON) += -mtune=pentium3 $(align) >+cflags-$(CONFIG_MCYRIXIII) += -mtune=c3 $(align) >+cflags-$(CONFIG_MVIAC3_2) += -mtune=c3-2 >+cflags-$(CONFIG_MVIAC7) += -mtune=i686 >+cflags-$(CONFIG_MATOM) += -mtune=atom >+cflags-$(CONFIG_MGEODEGX1) += -mtune=pentium-mmx >+cflags-$(CONFIG_MGEODE_LX) += -mtune=geode >+cflags-$(CONFIG_X86_GENERIC) += -mtune=generic > > # Bug fix for binutils: this option is required in order to keep > # binutils from generating NOPL instructions against our will. >diff --git a/arch/x86/include/asm/vermagic.h b/arch/x86/include/asm/vermagic.h >index e26061df0c9b..6554dbdfd719 100644 >--- a/arch/x86/include/asm/vermagic.h >+++ b/arch/x86/include/asm/vermagic.h >@@ -5,42 +5,10 @@ > > #ifdef CONFIG_X86_64 > /* X86_64 does not define MODULE_PROC_FAMILY */ >-#elif defined CONFIG_M586TSC >-#define MODULE_PROC_FAMILY "586TSC " >-#elif defined CONFIG_M586MMX >-#define MODULE_PROC_FAMILY "586MMX " >-#elif defined CONFIG_MATOM >-#define MODULE_PROC_FAMILY "ATOM " >-#elif defined CONFIG_M686 >+#elif defined CONFIG_X86_CMOV > #define MODULE_PROC_FAMILY "686 " >-#elif defined CONFIG_MPENTIUMII >-#define MODULE_PROC_FAMILY "PENTIUMII " >-#elif defined CONFIG_MPENTIUMIII >-#define MODULE_PROC_FAMILY "PENTIUMIII " >-#elif defined CONFIG_MPENTIUMM >-#define MODULE_PROC_FAMILY "PENTIUMM " >-#elif defined CONFIG_MPENTIUM4 >-#define MODULE_PROC_FAMILY "PENTIUM4 " >-#elif defined CONFIG_MK6 >-#define MODULE_PROC_FAMILY "K6 " >-#elif defined CONFIG_MK7 >-#define MODULE_PROC_FAMILY "K7 " >-#elif defined CONFIG_MCRUSOE >-#define MODULE_PROC_FAMILY "CRUSOE " >-#elif defined CONFIG_MEFFICEON >-#define MODULE_PROC_FAMILY "EFFICEON " >-#elif defined CONFIG_MCYRIXIII >-#define MODULE_PROC_FAMILY "CYRIXIII " >-#elif defined CONFIG_MVIAC3_2 >-#define MODULE_PROC_FAMILY "VIAC3-2 " >-#elif defined CONFIG_MVIAC7 >-#define MODULE_PROC_FAMILY "VIAC7 " >-#elif defined CONFIG_MGEODEGX1 >-#define MODULE_PROC_FAMILY "GEODEGX1 " >-#elif defined CONFIG_MGEODE_LX >-#define MODULE_PROC_FAMILY "GEODE " > #else >-#error unknown processor family >+#define MODULE_PROC_FAMILY "586 " > #endif > > #ifdef CONFIG_X86_32 >diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c >index 489c779ef3ef..76b15ef8c85f 100644 >--- a/arch/x86/kernel/tsc.c >+++ b/arch/x86/kernel/tsc.c >@@ -1221,7 +1221,7 @@ bool tsc_clocksource_watchdog_disabled(void) > > static void __init check_system_tsc_reliable(void) > { >-#if defined(CONFIG_MGEODEGX1) || defined(CONFIG_MGEODE_LX) || >defined(CONFIG_X86_GENERIC) >+#if defined(CONFIG_CPU_SUP_CYRIX) > if (is_geode_lx()) { > /* RTSC counts during suspend */ > #define RTSC_SUSP 0x100 >diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig >index 222b6fdad313..2648459b8e8f 100644 >--- a/arch/x86/xen/Kconfig >+++ b/arch/x86/xen/Kconfig >@@ -9,7 +9,6 @@ config XEN > select PARAVIRT_CLOCK > select X86_HV_CALLBACK_VECTOR > depends on X86_64 || (X86_32 && X86_PAE) >- depends on X86_64 || (X86_GENERIC || MPENTIUM4 || MATOM) > depends on X86_LOCAL_APIC > help > This is the Linux Xen port. Enabling this will allow the >diff --git a/drivers/misc/mei/Kconfig b/drivers/misc/mei/Kconfig >index 7575fee96cc6..4deb17ed0a62 100644 >--- a/drivers/misc/mei/Kconfig >+++ b/drivers/misc/mei/Kconfig >@@ -3,7 +3,7 @@ > config INTEL_MEI > tristate "Intel Management Engine Interface" > depends on X86 && PCI >- default X86_64 || MATOM >+ default X86_64 || CPU_SUP_INTEL > help > The Intel Management Engine (Intel ME) provides Manageability, > Security and Media services for system containing Intel chipsets. I really don't like testing an unrelated feature (CMOV for PAE); furthermore, at least some old hypervisors were known to have broken PAE. At the very least it needs to be abstracted for clarity reasons. Nacked-by: H. Peter Anvin <hpa@xxxxxxxxx>
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