Re: [PATCH RESEND 0/3] Represent cluster topology and enable load balance between clusters

[Peter Zijlstra]

On Sat, Oct 02, 2021 at 08:09:58PM +1300, Barry Song wrote:

> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7e4651a1aaf4..86821e83b935 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -993,8 +993,13 @@ 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. For example, on Hisilicon Kunpeng920, each 4 CPUs share
> +         LLC cache tags. This feature isn't a universal win because it
> +         can bring a cost of slightly increased overhead in some places.
> +         If unsure say N here.
> 
>  config SCHED_SMT
>         bool "SMT scheduler support"
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index bd27b1cdac34..940eb1fe0abb 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1002,12 +1002,17 @@ config NR_CPUS
>           to the kernel image.
> 
>  config SCHED_CLUSTER
> +       def_bool y
> +       prompt "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. For example, on x86 Jacobsville, each 4 CPUs share one
> +        L2 cache. 

			This feature isn't a universal win because it can bring
> +        a cost of slightly increased overhead in some places. If unsure
> +        say N here.

That is a really odd addition to a default-y feature.

How about I make both:

	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.