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

From: Peter Zijlstra <peterz@infradead.org>
To: Barry Song <21cnbao@gmail.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Ben Segall <bsegall@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Guodong Xu <guodong.xu@linaro.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	"Cc: Len Brown" <lenb@kernel.org>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	LAK <linux-arm-kernel@lists.infradead.org>,
	Linuxarm <linuxarm@huawei.com>,
	Mark Rutland <mark.rutland@arm.com>, Mel Gorman <mgorman@suse.de>,
	msys.mizuma@gmail.com, "Zengtao (B)" <prime.zeng@hisilicon.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Steven Rostedt <rostedt@goodmis.org>,
	Barry Song <song.bao.hua@hisilicon.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Will Deacon <will@kernel.org>, x86 <x86@kernel.org>,
	yangyicong <yangyicong@huawei.com>
Subject: Re: [PATCH RESEND 0/3] Represent cluster topology and enable load balance between clusters
Date: Tue, 5 Oct 2021 10:04:13 +0200	[thread overview]
Message-ID: <20211005080413.GL4323@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <CAGsJ_4wvLw=US1ddJr=Jrim1vs-F2hpcQ29LQyqDENd7Fk=ssA@mail.gmail.com>

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.