On Tue, Aug 26, 2025 at 10:07:06AM +0200, Peter Zijlstra wrote:
> On Tue, Aug 26, 2025 at 06:49:29AM +0200, Christophe Leroy wrote:
> >
> >
> > Le 26/08/2025 à 06:13, K Prateek Nayak a écrit :
> > > PowerPC enables the MC scheduling domain by default on systems with
> > > coregroup support without having a SCHED_MC config in Kconfig.
> > >
> > > The scheduler uses CONFIG_SCHED_MC to introduce the MC domain in the
> > > default topology (core) and to optimize the default CPU selection
> > > routine (sched-ext).
> > >
> > > Introduce CONFIG_SCHED_MC for powerpc and note that it should be
> > > preferably enabled given the current default behavior. This also ensures
> > > PowerPC is tested during future developments that come to depend on
> > > CONFIG_SCHED_MC.
> > >
> > > Signed-off-by: K Prateek Nayak <kprateek.na...@amd.com>
> > > ---
> > > arch/powerpc/Kconfig | 9 +++++++++
> > > arch/powerpc/include/asm/smp.h | 2 ++
> > > arch/powerpc/kernel/smp.c | 4 ++++
> > > 3 files changed, 15 insertions(+)
> > >
> > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > > index 93402a1d9c9f..e954ab3f635f 100644
> > > --- a/arch/powerpc/Kconfig
> > > +++ b/arch/powerpc/Kconfig
> > > @@ -971,6 +971,15 @@ config SCHED_SMT
> > > when dealing with POWER5 cpus at a cost of slightly increased
> > > overhead in some places. If unsure say N here.
> > > +config SCHED_MC
> > > + bool "Multi-Core Cache (MC) scheduler support"
> > > + depends on PPC64 && SMP
> > > + default y
> > > + help
> > > + MC scheduler support improves the CPU scheduler's decision making
> > > + when dealing with POWER systems that contain multiple Last Level
> > > + Cache instances on the same socket. If unsure say Y here.
> > > +
> >
> > You shouldn't duplicate CONFIG_SCHED_MC in every architecture, instead you
> > should define a CONFIG_ARCH_HAS_SCHED_MC in arch/Kconfig that gets selected
> > by architectures then have CONFIG_SCHED_MC defined in init/Kconfig or
> > kernel/Kconfig or so.
>
> Let me add this first -- it is currently duplicated. Then I'll see about
> merging the thing across architectures.
So what I added to power was:
config SCHED_MC
def_bool y
depends on PPC64 && SMP
because that is more or less the behaviour that was there, per the
existing SDTL_INIT().
---
Now, when I look at unifying those config options (there's a metric ton
of crap that's duplicated in the arch/*/Kconfig), I end up with something
like the below.
And while that isn't exact, it is the closest I could make it without
making a giant mess of things.
WDYT?
---
Kconfig | 38 ++++++++++++++++++++++++++++++++++++++
arm/Kconfig | 18 ++----------------
arm64/Kconfig | 26 +++-----------------------
loongarch/Kconfig | 19 ++-----------------
mips/Kconfig | 16 ++--------------
parisc/Kconfig | 9 +--------
powerpc/Kconfig | 15 +++------------
riscv/Kconfig | 9 +--------
s390/Kconfig | 8 ++------
sparc/Kconfig | 20 ++------------------
x86/Kconfig | 27 ++++-----------------------
11 files changed, 60 insertions(+), 145 deletions(-)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -41,6 +41,44 @@ config HOTPLUG_SMT
config SMT_NUM_THREADS_DYNAMIC
bool
+config ARCH_SUPPORTS_SCHED_SMT
+ bool
+
+config ARCH_SUPPORTS_SCHED_CLUSTER
+ bool
+
+config ARCH_SUPPORTS_SCHED_MC
+ bool
+
+config SCHED_SMT
+ bool "SMT (Hyperthreading) scheduler support"
+ depends on ARCH_SUPPORTS_SCHED_SMT
+ 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_CLUSTER
+ bool "Cluster scheduler support"
+ depends on ARCH_SUPPORTS_SCHED_CLUSTER
+ 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_MC
+ bool "Multi-Core Cache (MC) scheduler support"
+ depends on ARCH_SUPPORTS_SCHED_MC
+ 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.
+
# Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL
config HOTPLUG_CORE_SYNC
bool
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -941,28 +941,14 @@ config IRQSTACKS
config ARM_CPU_TOPOLOGY
bool "Support cpu topology definition"
depends on SMP && CPU_V7
+ select ARCH_SUPPORTS_SCHED_MC
+ select ARCH_SUPPORTS_SCHED_SMT
default y
help
Support ARM cpu topology definition. The MPIDR register defines
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
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -108,6 +108,9 @@ config ARM64
select ARCH_SUPPORTS_PER_VMA_LOCK
select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
select ARCH_SUPPORTS_RT
+ select ARCH_SUPPORTS_SCHED_SMT
+ select ARCH_SUPPORTS_SCHED_CLUSTER
+ select ARCH_SUPPORTS_SCHED_MC
select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
select ARCH_WANT_DEFAULT_BPF_JIT
@@ -1505,29 +1508,6 @@ 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
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -70,6 +70,8 @@ config LOONGARCH
select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
select ARCH_SUPPORTS_NUMA_BALANCING
select ARCH_SUPPORTS_RT
+ select ARCH_SUPPORTS_SCHED_SMT if SMP
+ select ARCH_SUPPORTS_SCHED_MC if SMP
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_USE_MEMTEST
@@ -448,23 +450,6 @@ config EFI_STUB
This kernel feature allows the kernel to be loaded directly by
EFI firmware without the use of a bootloader.
-config SCHED_SMT
- bool "SMT scheduler support"
- depends on SMP
- default y
- help
- Improves scheduler's performance when there are multiple
- threads in one physical core.
-
-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.
-
config SMP
bool "Multi-Processing support"
help
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2223,7 +2223,7 @@ config MIPS_MT_SMP
select SMP
select SMP_UP
select SYS_SUPPORTS_SMP
- select SYS_SUPPORTS_SCHED_SMT
+ select ARCH_SUPPORTS_SCHED_SMT
select MIPS_PERF_SHARED_TC_COUNTERS
help
This is a kernel model which is known as SMVP. This is supported
@@ -2235,18 +2235,6 @@ 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
-
config SYS_SUPPORTS_MULTITHREADING
bool
@@ -2318,7 +2306,7 @@ config MIPS_CPS
select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
select SYNC_R4K if (CEVT_R4K || CSRC_R4K)
select SYS_SUPPORTS_HOTPLUG_CPU
- select SYS_SUPPORTS_SCHED_SMT if CPU_MIPSR6
+ select ARCH_SUPPORTS_SCHED_SMT if CPU_MIPSR6
select SYS_SUPPORTS_SMP
select WEAK_ORDERING
select GENERIC_IRQ_MIGRATION if HOTPLUG_CPU
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -44,6 +44,7 @@ config PARISC
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select GENERIC_SMP_IDLE_THREAD
select GENERIC_ARCH_TOPOLOGY if SMP
+ select ARCH_SUPPORTS_SCHED_MC if SMP && PA8X00
select GENERIC_CPU_DEVICES if !SMP
select GENERIC_LIB_DEVMEM_IS_ALLOWED
select SYSCTL_ARCH_UNALIGN_ALLOW
@@ -319,14 +320,6 @@ config SMP
If you don't know what to do here, say N.
-config SCHED_MC
- bool "Multi-core scheduler support"
- depends on GENERIC_ARCH_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
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -170,6 +170,9 @@ config PPC
select ARCH_STACKWALK
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_DEBUG_PAGEALLOC if PPC_BOOK3S || PPC_8xx
+ select ARCH_SUPPORTS_SCHED_SMT if PPC64 && SMP
+ select ARCH_SUPPORTS_SCHED_MC if PPC64 && SMP
+ select SCHED_MC if ARCH_SUPPORTS_SCHED_MC
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF if PPC64
select ARCH_USE_MEMTEST
@@ -963,18 +966,6 @@ 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 SCHED_MC
- def_bool y
- depends on PPC64 && SMP
-
config PPC_DENORMALISATION
bool "PowerPC denormalisation exception handling"
depends on PPC_BOOK3S_64
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -72,6 +72,7 @@ config RISCV
select ARCH_SUPPORTS_PER_VMA_LOCK if MMU
select ARCH_SUPPORTS_RT
select ARCH_SUPPORTS_SHADOW_CALL_STACK if HAVE_SHADOW_CALL_STACK
+ select ARCH_SUPPORTS_SCHED_MC if SMP
select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
select ARCH_USE_MEMTEST
select ARCH_USE_QUEUED_RWLOCKS
@@ -453,14 +454,6 @@ config SMP
If you don't know what to do here, say N.
-config SCHED_MC
- bool "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 NR_CPUS
int "Maximum number of CPUs (2-512)"
depends on SMP
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -547,15 +547,11 @@ config NODES_SHIFT
depends on NUMA
default "1"
-config SCHED_SMT
- def_bool n
-
-config SCHED_MC
- def_bool n
-
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
help
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -110,6 +110,8 @@ config SPARC64
select HAVE_SETUP_PER_CPU_AREA
select NEED_PER_CPU_EMBED_FIRST_CHUNK
select NEED_PER_CPU_PAGE_FIRST_CHUNK
+ select ARCH_SUPPORTS_SCHED_SMT if SMP
+ select ARCH_SUPPORTS_SCHED_MC if SMP
config ARCH_PROC_KCORE_TEXT
def_bool y
@@ -288,24 +290,6 @@ if SPARC64 || COMPILE_TEST
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
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -330,6 +330,10 @@ config X86
imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI
select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
select ARCH_SUPPORTS_PT_RECLAIM if X86_64
+ select ARCH_SUPPORTS_SCHED_SMT if SMP
+ select SCHED_SMT if SMP
+ select ARCH_SUPPORTS_SCHED_CLUSTER if SMP
+ select ARCH_SUPPORTS_SCHED_MC if SMP
config INSTRUCTION_DECODER
def_bool y
@@ -1036,29 +1040,6 @@ 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
