From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EBF53C28CC0 for ; Thu, 30 May 2019 11:51:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6F462588A for ; Thu, 30 May 2019 11:51:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727007AbfE3LvP (ORCPT ); Thu, 30 May 2019 07:51:15 -0400 Received: from foss.arm.com ([217.140.101.70]:34882 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726792AbfE3LvO (ORCPT ); Thu, 30 May 2019 07:51:14 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E85B9374; Thu, 30 May 2019 04:51:13 -0700 (PDT) Received: from e105550-lin.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A814B3F5AF; Thu, 30 May 2019 04:51:09 -0700 (PDT) Date: Thu, 30 May 2019 12:51:03 +0100 From: Morten Rasmussen To: "Andrew F. Davis" Cc: Atish Patra , linux-kernel@vger.kernel.org, Sudeep Holla , Rob Herring , Albert Ou , Anup Patel , Catalin Marinas , "David S. Miller" , devicetree@vger.kernel.org, Greg Kroah-Hartman , Ingo Molnar , Jeremy Linton , Linus Walleij , linux-riscv@lists.infradead.org, Mark Rutland , Mauro Carvalho Chehab , Otto Sabart , Palmer Dabbelt , Paul Walmsley , "Peter Zijlstra (Intel)" , "Rafael J. Wysocki" , Rob Herring , Thomas Gleixner , Will Deacon , Russell King , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v6 1/7] Documentation: DT: arm: add support for sockets defining package boundaries Message-ID: <20190530115103.GA10919@e105550-lin.cambridge.arm.com> References: <20190529211340.17087-1-atish.patra@wdc.com> <20190529211340.17087-2-atish.patra@wdc.com> <49f41e62-5354-a674-d95f-5f63851a0ca6@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49f41e62-5354-a674-d95f-5f63851a0ca6@ti.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > > >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. At the moment user-space is only told about hw threads, cores, and sockets. In the very near future it is going to be told about dies too (look for Len Brown's multi-die patch set). I don't see how we can provide correct information to user-space based on the current information in DT. I'm not convinced it was a good idea to expose this information to user-space to begin with but that is another discussion. Morten