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,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 EDD60C04AB6 for ; Fri, 31 May 2019 09:41:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCFDB26702 for ; Fri, 31 May 2019 09:41:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726939AbfEaJlR (ORCPT ); Fri, 31 May 2019 05:41:17 -0400 Received: from foss.arm.com ([217.140.101.70]:48990 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726330AbfEaJlQ (ORCPT ); Fri, 31 May 2019 05:41:16 -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 A8520341; Fri, 31 May 2019 02:41:15 -0700 (PDT) Received: from e107155-lin (e107155-lin.cambridge.arm.com [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 44C313F59C; Fri, 31 May 2019 02:41:11 -0700 (PDT) Date: Fri, 31 May 2019 10:41:08 +0100 From: Sudeep Holla To: "Andrew F. Davis" Cc: Morten Rasmussen , Atish Patra , linux-kernel@vger.kernel.org, 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 , Sudeep Holla , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v6 1/7] Documentation: DT: arm: add support for sockets defining package boundaries Message-ID: <20190531094108.GC18292@e107155-lin> References: <20190529211340.17087-1-atish.patra@wdc.com> <20190529211340.17087-2-atish.patra@wdc.com> <49f41e62-5354-a674-d95f-5f63851a0ca6@ti.com> <20190530115103.GA10919@e105550-lin.cambridge.arm.com> <70639181-09d1-4644-f062-b19e06db7471@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <70639181-09d1-4644-f062-b19e06db7471@ti.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 30, 2019 at 08:56:03AM -0400, Andrew F. Davis wrote: > On 5/30/19 7:51 AM, 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 > > > > > > > > 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. > > > > I see the benefit of reporting the physical layout and packaging information > to user-space for tracking reasons, but from software perspective this > doesn't matter, and the resource partitioning should be described elsewhere > (NUMA nodes being the go to example). > > > 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). > > > > Seems my hypothetical case is already in the works :( > > > 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. > > > > Fair enough, it's a little late now to un-expose this info to userspace so > we should at least present it correctly. My worry was this getting out of > hand with layering, for instance what happens when we need to add die nodes > in-between cluster and socket? > We may have to, if there's a similar requirement on ARM64 as the one addressed by Len Brown's multi-die patch set. But for now, no one has asked for it. -- Regards, Sudeep