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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 00A8EEE49A0 for ; Tue, 22 Aug 2023 01:00:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231214AbjHVBAx (ORCPT ); Mon, 21 Aug 2023 21:00:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46822 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbjHVBAr (ORCPT ); Mon, 21 Aug 2023 21:00:47 -0400 Received: from mgamail.intel.com (mgamail.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 922CAD7; Mon, 21 Aug 2023 18:00:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1692666043; x=1724202043; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=PpIQtwVVDLgNvYt1ipLFOy1XV/k+n83Ca/rODVEtFaw=; b=JUWsQNKWf6AJdzsIvdMQ1EY0fW32TFu7VxCMze1FiLSOV1X/hq0HhJcu 6bG766P3T9SOfGJkZCV/M/9Ksh7Mbefz73ZXv8VUcfX8tgrhSBpZSRjH6 Q/Ce3ZldSuvSHNhwZOHILSSYQ8eLWO3jRnqBYHc6JqVWmlriYfSIL7amD LixXTCS4T+Vn7YMBhXL1k3GQM6bc+bC2cLWwFdPablQym4RjMuH2YTAOW 0QJROYpo+i67nEecDJ1gFG9MB2CH05vn05dtRAQhNOpAZ9VHrsLjEojBF o5PHOV6YDX08fWLECM4P2lbsQ/I8Izh+uv18E+KMEHylC5dtdx4EM3cEQ A==; X-IronPort-AV: E=McAfee;i="6600,9927,10809"; a="354072402" X-IronPort-AV: E=Sophos;i="6.01,191,1684825200"; d="scan'208";a="354072402" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Aug 2023 18:00:42 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10809"; a="685853988" X-IronPort-AV: E=Sophos;i="6.01,191,1684825200"; d="scan'208";a="685853988" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Aug 2023 18:00:35 -0700 From: "Huang, Ying" To: Alistair Popple Cc: Andrew Morton , , , , , , "Aneesh Kumar K . V" , Wei Xu , Dan Williams , Dave Hansen , "Davidlohr Bueso" , Johannes Weiner , "Jonathan Cameron" , Michal Hocko , Yang Shi , Rafael J Wysocki , Dave Jiang Subject: Re: [PATCH RESEND 1/4] memory tiering: add abstract distance calculation algorithms management References: <20230721012932.190742-1-ying.huang@intel.com> <20230721012932.190742-2-ying.huang@intel.com> <87r0owzqdc.fsf@nvdebian.thelocal> <87r0owy95t.fsf@yhuang6-desk2.ccr.corp.intel.com> <87sf9cxupz.fsf@nvdebian.thelocal> <878rb3xh2x.fsf@yhuang6-desk2.ccr.corp.intel.com> <87351axbk6.fsf@nvdebian.thelocal> <87edkuvw6m.fsf@yhuang6-desk2.ccr.corp.intel.com> <87y1j2vvqw.fsf@nvdebian.thelocal> <87a5vhx664.fsf@yhuang6-desk2.ccr.corp.intel.com> <87lef0x23q.fsf@nvdebian.thelocal> <87r0oack40.fsf@yhuang6-desk2.ccr.corp.intel.com> <87cyzgwrys.fsf@nvdebian.thelocal> <87il98c8ms.fsf@yhuang6-desk2.ccr.corp.intel.com> <87edjwlzn7.fsf@nvdebian.thelocal> Date: Tue, 22 Aug 2023 08:58:20 +0800 In-Reply-To: <87edjwlzn7.fsf@nvdebian.thelocal> (Alistair Popple's message of "Tue, 22 Aug 2023 09:52:43 +1000") Message-ID: <875y57dhar.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alistair Popple writes: > "Huang, Ying" writes: > >> Alistair Popple writes: >> >>> "Huang, Ying" writes: >>> >>>> Hi, Alistair, >>>> >>>> Sorry for late response. Just come back from vacation. >>> >>> Ditto for this response :-) >>> >>> I see Andrew has taken this into mm-unstable though, so my bad for not >>> getting around to following all this up sooner. >>> >>>> Alistair Popple writes: >>>> >>>>> "Huang, Ying" writes: >>>>> >>>>>> Alistair Popple writes: >>>>>> >>>>>>> "Huang, Ying" writes: >>>>>>> >>>>>>>> Alistair Popple writes: >>>>>>>> >>>>>>>>>>>> While other memory device drivers can use the general notifier chain >>>>>>>>>>>> interface at the same time. >>>>>>>>> >>>>>>>>> How would that work in practice though? The abstract distance as far as >>>>>>>>> I can tell doesn't have any meaning other than establishing preferences >>>>>>>>> for memory demotion order. Therefore all calculations are relative to >>>>>>>>> the rest of the calculations on the system. So if a driver does it's own >>>>>>>>> thing how does it choose a sensible distance? IHMO the value here is in >>>>>>>>> coordinating all that through a standard interface, whether that is HMAT >>>>>>>>> or something else. >>>>>>>> >>>>>>>> Only if different algorithms follow the same basic principle. For >>>>>>>> example, the abstract distance of default DRAM nodes are fixed >>>>>>>> (MEMTIER_ADISTANCE_DRAM). The abstract distance of the memory device is >>>>>>>> in linear direct proportion to the memory latency and inversely >>>>>>>> proportional to the memory bandwidth. Use the memory latency and >>>>>>>> bandwidth of default DRAM nodes as base. >>>>>>>> >>>>>>>> HMAT and CDAT report the raw memory latency and bandwidth. If there are >>>>>>>> some other methods to report the raw memory latency and bandwidth, we >>>>>>>> can use them too. >>>>>>> >>>>>>> Argh! So we could address my concerns by having drivers feed >>>>>>> latency/bandwidth numbers into a standard calculation algorithm right? >>>>>>> Ie. Rather than having drivers calculate abstract distance themselves we >>>>>>> have the notifier chains return the raw performance data from which the >>>>>>> abstract distance is derived. >>>>>> >>>>>> Now, memory device drivers only need a general interface to get the >>>>>> abstract distance from the NUMA node ID. In the future, if they need >>>>>> more interfaces, we can add them. For example, the interface you >>>>>> suggested above. >>>>> >>>>> Huh? Memory device drivers (ie. dax/kmem.c) don't care about abstract >>>>> distance, it's a meaningless number. The only reason they care about it >>>>> is so they can pass it to alloc_memory_type(): >>>>> >>>>> struct memory_dev_type *alloc_memory_type(int adistance) >>>>> >>>>> Instead alloc_memory_type() should be taking bandwidth/latency numbers >>>>> and the calculation of abstract distance should be done there. That >>>>> resovles the issues about how drivers are supposed to devine adistance >>>>> and also means that when CDAT is added we don't have to duplicate the >>>>> calculation code. >>>> >>>> In the current design, the abstract distance is the key concept of >>>> memory types and memory tiers. And it is used as interface to allocate >>>> memory types. This provides more flexibility than some other interfaces >>>> (e.g. read/write bandwidth/latency). For example, in current >>>> dax/kmem.c, if HMAT isn't available in the system, the default abstract >>>> distance: MEMTIER_DEFAULT_DAX_ADISTANCE is used. This is still useful >>>> to support some systems now. On a system without HMAT/CDAT, it's >>>> possible to calculate abstract distance from ACPI SLIT, although this is >>>> quite limited. I'm not sure whether all systems will provide read/write >>>> bandwith/latency data for all memory devices. >>>> >>>> HMAT and CDAT or some other mechanisms may provide the read/write >>>> bandwidth/latency data to be used to calculate abstract distance. For >>>> them, we can provide a shared implementation in mm/memory-tiers.c to map >>>> from read/write bandwith/latency to the abstract distance. Can this >>>> solve your concerns about the consistency among algorithms? If so, we >>>> can do that when we add the second algorithm that needs that. >>> >>> I guess it would address my concerns if we did that now. I don't see why >>> we need to wait for a second implementation for that though - the whole >>> series seems to be built around adding a framework for supporting >>> multiple algorithms even though only one exists. So I think we should >>> support that fully, or simplfy the whole thing and just assume the only >>> thing that exists is HMAT and get rid of the general interface until a >>> second algorithm comes along. >> >> We will need a general interface even for one algorithm implementation. >> Because it's not good to make a dax subsystem driver (dax/kmem) to >> depend on a ACPI subsystem driver (acpi/hmat). We need some general >> interface at subsystem level (memory tier here) between them. > > I don't understand this argument. For a single algorithm it would be > simpler to just define acpi_hmat_calculate_adistance() and a static > inline version of it that returns -ENOENT when !CONFIG_ACPI than adding > a layer of indirection through notifier blocks. That breaks any > dependency on ACPI and there's plenty of precedent for this approach in > the kernel already. ACPI is a subsystem, so it's OK for dax/kmem to depends on CONFIG_ACPI. But HMAT is a driver of ACPI subsystem (controlled via CONFIG_ACPI_HMAT). It's not good for a driver of DAX subsystem (dax/kmem) to depend on a *driver* of ACPI subsystem. Yes. Technically, there's no hard wall to prevent this. But I think that a good design should make drivers depends on subsystems or drivers of the same subsystem, NOT drivers of other subsystems. -- Best Regards, Huang, Ying