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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1x11ob-00000009sFC-353M; Mon, 31 Aug 2026 13:12:46 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 918B9300E7E; Mon, 31 Aug 2026 15:12:44 +0200 (CEST) Date: Mon, 31 Aug 2026 15:12:44 +0200 From: Peter Zijlstra To: Jianyong Wu Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Chen Yu , Tim Chen , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Shrikanth Hegde , Phil Auld , Andrew Morton , David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, jianyong.wu@outlook.com, zhongyuan@hygon.cn, huangsj@hygon.cn, wangfengyu@hygon.cn, yingzhiwei@hygon.cn, justin.he@arm.com Subject: Re: [RFC PATCH v2 04/23] sched/topology: Introduce a method to calculate the llc distance Message-ID: <20260831131244.GJ4120091@noisy.programming.kicks-ass.net> References: <20260827122816.756234-1-wujianyong@hygon.cn> <20260827122816.756234-5-wujianyong@hygon.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260827122816.756234-5-wujianyong@hygon.cn> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2E64680006 X-Stat-Signature: suggd9e1599w63xsgn9fdpaocgpxf5ps X-HE-Tag: 1788181975-324513 X-HE-Meta: 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 T9aqLXaS Hys69un6pvXesMnjCEdaFH5QPNDhqpoM5O5PTVEKM/bRvOQUESkpF4/kK+CeLkJfpwGt4Zk3jKkCCfRyz/9iG0v8zU6QxjSWK+QJpnRoe8TXeK8RpvyqdMlki1ZsNsIABN5L4Aw657JZrJCDmowiWFjsSJULGrsrT8EQJUw3qfw0wiJplM0Ke2m3C+aIdmFwydPVCdfUQC2gzDOLPyidxNnz9yrDJF+rGonub4FFQrdIVOrY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 27, 2026 at 08:27:57PM +0800, Jianyong Wu wrote: > The previous patch addresses NUMA inter-node distance handling. This > patch shifts focus to the LLC layer and introduces a scheme to compute > pairwise distances between sibling LLCs inside one NUMA node. > The calculation only guarantees distinct distance values for all peers > when viewed from a single reference LLC; it does not enforce globally > unique distances for every arbitrary LLC pair on the node. > > One valid calculation scheme is defined by the formula below: > > dist(LLC1, LLC2) = (rank1 + rank2) % k + 1 > > Constraints: LLC1 and LLC2 must reside on the identical NUMA node. > rank1 = local index of LLC1 within its node; rank2 follows the same rule. > k = total count of LLCs available on the node. > > The formula never yields zero, so diagonal self-distance entries are > explicitly hardcoded to 0. > > For demonstration, consider a NUMA node with four LLCs (local ranks 0~3): > LLC0 LLC1 LLC2 LLC3 > LLC0 0 2 3 4 > LLC1 2 0 4 1 > LLC2 3 4 0 2 > LLC3 4 1 2 0 > > Sorting each matrix row in ascending order generates a unique LLC affinity > sequence, which drives thread migration policies implemented in follow-up > patches. Aah, now I see. I got confused by your sched_cache_node_distance naming, and thought it was cache-to-cache distance.