From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 104001A58C for ; Fri, 3 Nov 2023 14:16:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9955E1B9; Fri, 3 Nov 2023 07:16:41 -0700 (PDT) Received: from lhrpeml500005.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4SMN505bbhz689SY; Fri, 3 Nov 2023 22:13:24 +0800 (CST) Received: from localhost (10.202.227.76) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.31; Fri, 3 Nov 2023 14:16:37 +0000 Date: Fri, 3 Nov 2023 14:16:36 +0000 From: Jonathan Cameron To: "Huang, Ying" , Gregory Price CC: Michal Hocko , Johannes Weiner , Gregory Price , , , , , , , , , , , , Subject: Re: [RFC PATCH v3 0/4] Node Weights and Weighted Interleave Message-ID: <20231103141636.000007e4@Huawei.com> In-Reply-To: <87fs1nz3ee.fsf@yhuang6-desk2.ccr.corp.intel.com> References: <20231031003810.4532-1-gregory.price@memverge.com> <20231031152142.GA3029315@cmpxchg.org> <87fs1nz3ee.fsf@yhuang6-desk2.ccr.corp.intel.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.227.76] X-ClientProxiedBy: lhrpeml500004.china.huawei.com (7.191.163.9) To lhrpeml500005.china.huawei.com (7.191.163.240) X-CFilter-Loop: Reflected On Fri, 03 Nov 2023 15:45:13 +0800 "Huang, Ying" wrote: > Gregory Price writes: > > > On Thu, Nov 02, 2023 at 10:47:33AM +0100, Michal Hocko wrote: > >> On Wed 01-11-23 12:58:55, Gregory Price wrote: > >> > Basically consider: `numactl --interleave=all ...` > >> > > >> > If `--weights=...`: when a node hotplug event occurs, there is no > >> > recourse for adding a weight for the new node (it will default to 1). > >> > >> Correct and this is what I was asking about in an earlier email. How > >> much do we really need to consider this setup. Is this something nice to > >> have or does the nature of the technology requires to be fully dynamic > >> and expect new nodes coming up at any moment? > >> > > > > Dynamic Capacity is expected to cause a numa node to change size (in > > number of memory blocks) rather than cause numa nodes to come and go, so > > maybe handling the full node hotplug is a bit of an overreach. > > Will node max bandwidth change with the number of memory blocks? Typically no as even a single memory extent would probably be interleaved across all the actual memory devices (think DIMMS for simplicity) within a CXL device. I guess a device 'could' do some scaling based on capacity provided to a particular host but feels like they should be separate controls. I don't recall there being anything in the specification to suggest the need to recheck the CDAT info for updates when DC add / remove events happen. Mind you, who knows in future :) We'll point out in relevant forums that doing so would be very hard to handle cleanly in Linux. Jonathan