Re: [PATCH v7 4/8] powerpc/smp: Introduce CONFIG_SCHED_MC to guard MC scheduling bits

[Shrikanth Hegde <sshegde@linux.ibm.com>]

Hi Peter.

Looking at this,
https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=sched/core&id=9d710c5b2bb37cedf5f09ce988884fb5795e1a76

> 
> 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

...

> --- 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

Wondering if this SCHED_MC is necessary here? shouldn't it be set by arch/Kconfig?

nit: Also, can we have so they are still sorted?
	select ARCH_SUPPORTS_SCHED_MC		if PPC64 && SMP
	select ARCH_SUPPORTS_SCHED_SMT		if PPC64 && SMP

>   	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
Same here. Above two are needed?

>   	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
Is this SCHED_SMT needed here?

> +	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