[PATCH 2/2] sched: Centralize SCHED_{SMT, MC, CLUSTER} definitions

Valentin Schneider
2021-10-08T11:54:51Z

Barry recently introduced a new CONFIG_SCHED_CLUSTER, and discussions
around that highlighted that every architecture redefines its own help text
and dependencies for CONFIG_SCHED_SMT and CONFIG_SCHED_MC.

Move the definition of those to scheduler's Kconfig to centralize help text
and generic dependencies (i.e. SMP). Make them depend on a matching
ARCH_SUPPORTS_SCHED_* which the architectures can select with the relevant
architecture-specific dependency.

s390 uses its own topology table (set_sched_topology()) and doesn't seem to
cope without SCHED_MC or SCHED_SMT, so those remain untogglable.

Suggested-by: Barry Song <21cnbao@gmail.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
arch/arm/Kconfig | 18 ++----------------
arch/arm64/Kconfig | 26 +++-----------------------
arch/ia64/Kconfig | 9 +--------
arch/mips/Kconfig | 10 +---------
arch/parisc/Kconfig | 9 +--------
arch/powerpc/Kconfig | 9 +--------
arch/s390/Kconfig | 8 ++------
arch/sh/Kconfig | 1 +
arch/sh/mm/Kconfig | 9 ---------
arch/sparc/Kconfig | 20 ++------------------
arch/x86/Kconfig | 26 +++-----------------------
kernel/sched/Kconfig | 43 +++++++++++++++++++++++++++++++++++++++++++
12 files changed, 60 insertions(+), 128 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fc196421b2ce..13aac98edf06 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -32,6 +32,8 @@ config ARM
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
+ select ARCH_SUPPORTS_SCHED_SMT if ARM_CPU_TOPOLOGY
+ select ARCH_SUPPORTS_SCHED_MC if ARM_CPU_TOPOLOGY
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_USE_MEMTEST
@@ -1166,22 +1168,6 @@ config ARM_CPU_TOPOLOGY
affinity between processors which is then used to describe the cpu
topology of an ARM System.

-config SCHED_MC
- bool "Multi-core scheduler support"
- depends on ARM_CPU_TOPOLOGY
- help
- Multi-core scheduler support improves the CPU scheduler's decision
- making when dealing with multi-core CPU chips at a cost of slightly
- increased overhead in some places. If unsure say N here.
-
-config SCHED_SMT
- bool "SMT scheduler support"
- depends on ARM_CPU_TOPOLOGY
- help
- Improves the CPU scheduler's decision making when dealing with
- MultiThreading at a cost of slightly increased overhead in some
- places. If unsure say N here.
-
config HAVE_ARM_SCU
bool
help
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index d13677f4731d..8a49dd33f5e3 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -88,6 +88,9 @@ config ARM64
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
select ARCH_SUPPORTS_NUMA_BALANCING
+ select ARCH_SUPPORTS_SCHED_SMT
+ select ARCH_SUPPORTS_SCHED_MC
+ select ARCH_SUPPORTS_SCHED_CLUSTER
select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
select ARCH_WANT_DEFAULT_BPF_JIT
select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
@@ -982,29 +985,6 @@ config CPU_LITTLE_ENDIAN

endchoice

-config SCHED_MC
- bool "Multi-core scheduler support"
- help
- Multi-core scheduler support improves the CPU scheduler's decision
- making when dealing with multi-core CPU chips at a cost of slightly
- increased overhead in some places. If unsure say N here.
-
-config SCHED_CLUSTER
- bool "Cluster scheduler support"
- help
- Cluster scheduler support improves the CPU scheduler's decision
- making when dealing with machines that have clusters of CPUs.
- Cluster usually means a couple of CPUs which are placed closely
- by sharing mid-level caches, last-level cache tags or internal
- busses.
-
-config SCHED_SMT
- bool "SMT scheduler support"
- help
- Improves the CPU scheduler's decision making when dealing with
- MultiThreading at a cost of slightly increased overhead in some
- places. If unsure say N here.
-
config NR_CPUS
int "Maximum number of CPUs (2-4096)"
range 2 4096
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 045792cde481..67f3d84242ae 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -18,6 +18,7 @@ config IA64
select ARCH_ENABLE_MEMORY_HOTPLUG
select ARCH_ENABLE_MEMORY_HOTREMOVE
select ARCH_SUPPORTS_ACPI
+ select ARCH_SUPPORTS_SCHED_SMT
select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
select ARCH_MIGHT_HAVE_ACPI_PDC if ACPI
select FORCE_PCI
@@ -247,14 +248,6 @@ config HOTPLUG_CPU
can be controlled through /sys/devices/system/cpu/cpu#.
Say N if you want to disable CPU hotplug.

-config SCHED_SMT
- bool "SMT scheduler support"
- depends on SMP
- help
- Improves the CPU scheduler's decision making when dealing with
- Intel IA64 chips with MultiThreading at a cost of slightly increased
- overhead in some places. If unsure say N here.
-
config PERMIT_BSP_REMOVE
bool "Support removal of Bootstrap Processor"
depends on HOTPLUG_CPU
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 771ca53af06d..cc60d440b097 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2373,17 +2373,9 @@ config MIPS_MT_SMP
config MIPS_MT
bool

-config SCHED_SMT
- bool "SMT (multithreading) scheduler support"
- depends on SYS_SUPPORTS_SCHED_SMT
- default n
- help
- SMT scheduler support improves the CPU scheduler's decision making
- when dealing with MIPS MT enabled cores at a cost of slightly
- increased overhead in some places. If unsure say N here.
-
config SYS_SUPPORTS_SCHED_SMT
bool
+ select ARCH_SUPPORTS_SCHED_SMT

config SYS_SUPPORTS_MULTITHREADING
bool
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 4742b6f169b7..6aaa962ec2f4 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -13,6 +13,7 @@ config PARISC
select ARCH_NO_SG_CHAIN
select ARCH_SUPPORTS_HUGETLBFS if PA20
select ARCH_SUPPORTS_MEMORY_FAILURE
+ select ARCH_SUPPORTS_SCHED_MC if PARISC_CPU_TOPOLOGY && PA8X00
select DMA_OPS
select RTC_CLASS
select RTC_DRV_GENERIC
@@ -295,14 +296,6 @@ config PARISC_CPU_TOPOLOGY
help
Support PARISC cpu topology definition.

-config SCHED_MC
- bool "Multi-core scheduler support"
- depends on PARISC_CPU_TOPOLOGY && PA8X00
- help
- Multi-core scheduler support improves the CPU scheduler's decision
- making when dealing with multi-core CPU chips at a cost of slightly
- increased overhead in some places. If unsure say N here.
-
config IRQSTACKS
bool "Use separate kernel stacks when processing interrupts"
default y
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index ba5b66189358..9f45b92ccac1 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -151,6 +151,7 @@ config PPC
select ARCH_STACKWALK
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_DEBUG_PAGEALLOC if PPC32 || PPC_BOOK3S_64
+ select ARCH_SUPPORTS_SCHED_SMT if PPC64
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF if PPC64
select ARCH_USE_MEMTEST
@@ -861,14 +862,6 @@ config PPC_PROT_SAO_LPAR
config PPC_COPRO_BASE
bool

-config SCHED_SMT
- bool "SMT (Hyperthreading) scheduler support"
- depends on PPC64 && SMP
- help
- SMT scheduler support improves the CPU scheduler's decision making
- when dealing with POWER5 cpus at a cost of slightly increased
- overhead in some places. If unsure say N here.
-
config PPC_DENORMALISATION
bool "PowerPC denormalisation exception handling"
depends on PPC_BOOK3S_64
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index b86de61b8caa..a0b4117cb1fa 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -483,12 +483,6 @@ config NODES_SHIFT
depends on NUMA
default "1"

-config SCHED_SMT
- def_bool n
-
-config SCHED_MC
- def_bool n
-
config SCHED_BOOK
def_bool n

@@ -498,6 +492,8 @@ config SCHED_DRAWER
config SCHED_TOPOLOGY
def_bool y
prompt "Topology scheduler support"
+ select ARCH_SUPPORTS_SCHED_SMT
+ select ARCH_SUPPORTS_SCHED_MC
select SCHED_SMT
select SCHED_MC
select SCHED_BOOK
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 6904f4bdbf00..7380ee27d252 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -13,6 +13,7 @@ config SUPERH
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
select ARCH_HIBERNATION_POSSIBLE if MMU
select ARCH_MIGHT_HAVE_PC_PARPORT
+ select ARCH_SUPPORTS_SCHED_MC
select ARCH_WANT_IPC_PARSE_VERSION
select CPU_NO_EFFICIENT_FFS
select DMA_DECLARE_COHERENT
diff --git a/arch/sh/mm/Kconfig b/arch/sh/mm/Kconfig
index ba569cfb4368..1d9f7006a72a 100644
--- a/arch/sh/mm/Kconfig
+++ b/arch/sh/mm/Kconfig
@@ -208,15 +208,6 @@ config HUGETLB_PAGE_SIZE_64MB

endchoice

-config SCHED_MC
- bool "Multi-core scheduler support"
- depends on SMP
- default y
- help
- Multi-core scheduler support improves the CPU scheduler's decision
- making when dealing with multi-core CPU chips at a cost of slightly
- increased overhead in some places. If unsure say N here.
-
endmenu

menu "Cache configuration"
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index b120ed947f50..a6cf30d37725 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -86,6 +86,8 @@ config SPARC64
select HAVE_ARCH_AUDITSYSCALL
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_DEBUG_PAGEALLOC
+ select ARCH_SUPPORTS_SCHED_SMT
+ select ARCH_SUPPORTS_SCHED_MC
select HAVE_NMI
select HAVE_REGS_AND_STACK_ACCESS_API
select ARCH_USE_QUEUED_RWLOCKS
@@ -290,24 +292,6 @@ if SPARC64
source "kernel/power/Kconfig"
endif

-config SCHED_SMT
- bool "SMT (Hyperthreading) scheduler support"
- depends on SPARC64 && SMP
- default y
- help
- SMT scheduler support improves the CPU scheduler's decision making
- when dealing with SPARC cpus at a cost of slightly increased overhead
- in some places. If unsure say N here.
-
-config SCHED_MC
- bool "Multi-core scheduler support"
- depends on SPARC64 && SMP
- default y
- help
- Multi-core scheduler support improves the CPU scheduler's decision
- making when dealing with multi-core CPU chips at a cost of slightly
- increased overhead in some places. If unsure say N here.
-
config CMDLINE_BOOL
bool "Default bootloader kernel arguments"
depends on SPARC64
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 349e59b2f0e3..87a91fd33d85 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -107,6 +107,9 @@ config X86
select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP if NR_CPUS <= 4096
select ARCH_SUPPORTS_LTO_CLANG
select ARCH_SUPPORTS_LTO_CLANG_THIN
+ select ARCH_SUPPORTS_SCHED_SMT
+ select ARCH_SUPPORTS_SCHED_MC
+ select ARCH_SUPPORTS_SCHED_CLUSTER
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_MEMTEST
select ARCH_USE_QUEUED_RWLOCKS
@@ -1001,29 +1004,6 @@ config NR_CPUS
This is purely to save memory: each supported CPU adds about 8KB
to the kernel image.

-config SCHED_CLUSTER
- bool "Cluster scheduler support"
- depends on SMP
- default y
- help
- Cluster scheduler support improves the CPU scheduler's decision
- making when dealing with machines that have clusters of CPUs.
- Cluster usually means a couple of CPUs which are placed closely
- by sharing mid-level caches, last-level cache tags or internal
- busses.
-
-config SCHED_SMT
- def_bool y if SMP
-
-config SCHED_MC
- def_bool y
- prompt "Multi-core scheduler support"
- depends on SMP
- help
- Multi-core scheduler support improves the CPU scheduler's decision
- making when dealing with multi-core CPU chips at a cost of slightly
- increased overhead in some places. If unsure say N here.
-
config SCHED_MC_PRIO
bool "CPU core priorities scheduler support"
depends on SCHED_MC && CPU_SUP_INTEL
diff --git a/kernel/sched/Kconfig b/kernel/sched/Kconfig
index c8b8e12c9c9c..9ceb08f42aeb 100644
--- a/kernel/sched/Kconfig
+++ b/kernel/sched/Kconfig
@@ -131,3 +131,46 @@ config SCHED_CORE
SCHED_CORE is default disabled. When it is enabled and unused,
which is the likely usage by Linux distributions, there should
be no measurable impact on performance.
+
+
+#
+# For architectuers that want to enable generic scheduler handling of
+# different topology levels:
+#
+config ARCH_SUPPORTS_SCHED_SMT
+ bool
+
+config ARCH_SUPPORTS_SCHED_MC
+ bool
+
+config ARCH_SUPPORTS_SCHED_CLUSTER
+ bool
+
+config SCHED_SMT
+ bool "SMT scheduler support"
+ depends on ARCH_SUPPORTS_SCHED_SMT && SMP
+ default y
+ help
+ Improves the CPU scheduler's decision making when dealing with
+ MultiThreading at a cost of slightly increased overhead in some
+ places. If unsure say N here.
+
+config SCHED_MC
+ bool "Multi-core scheduler support"
+ depends on ARCH_SUPPORTS_SCHED_MC && SMP
+ default y
+ help
+ Multi-core scheduler support improves the CPU scheduler's decision
+ making when dealing with multi-core CPU chips at a cost of slightly
+ increased overhead in some places. If unsure say N here.
+
+config SCHED_CLUSTER
+ bool "Cluster scheduler support"
+ depends on ARCH_SUPPORTS_SCHED_CLUSTER && SMP
+ default y
+ help
+ Cluster scheduler support improves the CPU scheduler's decision
+ making when dealing with machines that have clusters of CPUs.
+ Cluster usually means a couple of CPUs which are placed closely
+ by sharing mid-level caches, last-level cache tags or internal
+ busses.
--
2.25.1