Re: [PATCH v6 1/7] Documentation: DT: arm: add support for sockets defining package boundaries - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Peter Zijlstra \(Intel\)" <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Palmer Dabbelt <palmer@sifive.com>,
	Will Deacon <will.deacon@arm.com>,
	Atish Patra <atish.patra@wdc.com>,
	Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
	linux-riscv@lists.infradead.org, Ingo Molnar <mingo@kernel.org>,
	Rob Herring <robh@kernel.org>, Anup Patel <anup@brainfault.org>,
	devicetree@vger.kernel.org, Albert Ou <aou@eecs.berkeley.edu>,
	Rob Herring <robh+dt@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org,
	Jeremy Linton <jeremy.linton@arm.com>,
	"Andrew F. Davis" <afd@ti.com>,
	Otto Sabart <ottosabart@seberm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH v6 1/7] Documentation: DT: arm: add support for sockets defining package boundaries
Date: Thu, 30 May 2019 22:42:54 +0100	[thread overview]
Message-ID: <20190530214254.tuxsnyv52a2fyhck@shell.armlinux.org.uk> (raw)
In-Reply-To: <20190530115103.GA10919@e105550-lin.cambridge.arm.com>

On Thu, May 30, 2019 at 12:51:03PM +0100, Morten Rasmussen wrote:
> On Wed, May 29, 2019 at 07:39:17PM -0400, Andrew F. Davis wrote:
> > On 5/29/19 5:13 PM, Atish Patra wrote:
> > >From: Sudeep Holla <sudeep.holla@arm.com>
> > >
> > >The current ARM DT topology description provides the operating system
> > >with a topological view of the system that is based on leaf nodes
> > >representing either cores or threads (in an SMT system) and a
> > >hierarchical set of cluster nodes that creates a hierarchical topology
> > >view of how those cores and threads are grouped.
> > >
> > >However this hierarchical representation of clusters does not allow to
> > >describe what topology level actually represents the physical package or
> > >the socket boundary, which is a key piece of information to be used by
> > >an operating system to optimize resource allocation and scheduling.
> > >
> > 
> > Are physical package descriptions really needed? What does "socket" imply
> > that a higher layer "cluster" node grouping does not? It doesn't imply a
> > different NUMA distance and the definition of "socket" is already not well
> > defined, is a dual chiplet processor not just a fancy dual "socket" or are
> > dual "sockets" on a server board "slotket" card, will we need new names for
> > those too..
> 
> Socket (or package) just implies what you suggest, a grouping of CPUs
> based on the physical socket (or package). Some resources might be
> associated with packages and more importantly socket information is
> exposed to user-space. At the moment clusters are being exposed to
> user-space as sockets which is less than ideal for some topologies.

Please point out a 32-bit ARM system that has multiple "socket"s.

As far as I'm aware, all 32-bit systems do not have socketed CPUs
(modern ARM CPUs are part of a larger SoC), and the CPUs are always
in one package.

Even the test systems I've seen do not have socketed CPUs.

-- 
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