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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 31EF5C43387 for ; Wed, 9 Jan 2019 17:48:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F118520665 for ; Wed, 9 Jan 2019 17:48:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727341AbfAIRsH (ORCPT ); Wed, 9 Jan 2019 12:48:07 -0500 Received: from mga11.intel.com ([192.55.52.93]:34829 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727271AbfAIRsE (ORCPT ); Wed, 9 Jan 2019 12:48:04 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Jan 2019 09:48:02 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,458,1539673200"; d="scan'208";a="115485663" Received: from unknown (HELO localhost.lm.intel.com) ([10.232.112.69]) by fmsmga008.fm.intel.com with ESMTP; 09 Jan 2019 09:48:02 -0800 From: Keith Busch To: linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-mm@kvack.org Cc: Greg Kroah-Hartman , Rafael Wysocki , Dave Hansen , Dan Williams , Keith Busch Subject: [PATCHv3 13/13] doc/mm: New documentation for memory performance Date: Wed, 9 Jan 2019 10:43:41 -0700 Message-Id: <20190109174341.19818-14-keith.busch@intel.com> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20190109174341.19818-1-keith.busch@intel.com> References: <20190109174341.19818-1-keith.busch@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Platforms may provide system memory where some physical address ranges perform differently than others, or is side cached by the system. Add documentation describing a high level overview of such systems and the perforamnce and caching attributes the kernel provides for applications wishing to query this information. Signed-off-by: Keith Busch --- Documentation/admin-guide/mm/numaperf.rst | 184 ++++++++++++++++++++++++++++++ 1 file changed, 184 insertions(+) create mode 100644 Documentation/admin-guide/mm/numaperf.rst diff --git a/Documentation/admin-guide/mm/numaperf.rst b/Documentation/admin-guide/mm/numaperf.rst new file mode 100644 index 000000000000..b6d99d7e0f57 --- /dev/null +++ b/Documentation/admin-guide/mm/numaperf.rst @@ -0,0 +1,184 @@ +.. _numaperf: + +============= +NUMA Locality +============= + +Some platforms may have multiple types of memory attached to a single +CPU. These disparate memory ranges share some characteristics, such as +CPU cache coherence, but may have different performance. For example, +different media types and buses affect bandwidth and latency. + +A system supporting such heterogeneous memory by grouping each memory +type under different "nodes" based on similar CPU locality and performance +characteristics. Some memory may share the same node as a CPU, and others +are provided as memory only nodes. While memory only nodes do not provide +CPUs, they may still be directly accessible, or local, to one or more +compute nodes. The following diagram shows one such example of two compute +noes with local memory and a memory only node for each of compute node: + + +------------------+ +------------------+ + | Compute Node 0 +-----+ Compute Node 1 | + | Local Node0 Mem | | Local Node1 Mem | + +--------+---------+ +--------+---------+ + | | + +--------+---------+ +--------+---------+ + | Slower Node2 Mem | | Slower Node3 Mem | + +------------------+ +--------+---------+ + +A "memory initiator" is a node containing one or more devices such as +CPUs or separate memory I/O devices that can initiate memory requests. A +"memory target" is a node containing one or more accessible physical +address ranges from one or more memory initiators. + +When multiple memory initiators exist, they may not all have the same +performance when accessing a given memory target. Each initiator-target +pair may be organized into different ranked access classes to represent +this relationship. The highest performing initiator to a given target +is considered to be one of that target's local initiators, and given +the highest access class, 0. Any given target may have one or more +local initiators, and any given initiator may have multiple local +memory targets. + +To aid applications matching memory targets with their initiators, the +kernel provide symlinks to each other. The following example lists the +relationship for the class "0" memory intiators and targets, which is +are the class of nodes with the highest performing access relationship:: + + # symlinks -v /sys/devices/system/node/nodeX/class0/ + relative: /sys/devices/system/node/nodeX/class0/targetY -> ../../nodeY + + # symlinks -v /sys/devices/system/node/nodeY/class0/ + relative: /sys/devices/system/node/nodeY/class0/initiatorX -> ../../nodeX + +The linked nodes will also have their node numbers set in the class's +mem_target and mem_initiator nodelist and nodemap entries. Following +the same example as above may look like the following:: + + # cat /sys/devices/system/node/nodeX/class0/target_nodelist + Y + + # cat /sys/devices/system/node/nodeY/class0/initiator_nodelist + X + +An example showing how this may be used to run a particular task on CPUs +and memory using best class nodes for a particular PCI device can be done +using existing 'numactl' as follows:: + + # NODE=$(cat /sys/devices/pci:0000:00/.../numa_node) + # numactl --membind=$(cat /sys/devices/node/node${NODE}/class0/target_nodelist) \ + --cpunodebind=$(cat /sys/devices/node/node${NODE}/class0/initiator_nodelist) \ + -- + +================ +NUMA Performance +================ + +Applications may wish to consider which node they want their memory to +be allocated from based on the node's performance characteristics. If +the system provides these attributes, the kernel exports them under the +node sysfs hierarchy by appending the attributes directory under the +memory node's class 0 initiators as follows:: + + /sys/devices/system/node/nodeY/class0/ + +These attributes apply only to the memory initiator nodes that have the +same class access and are symlink under the class, and are set in the +initiators' nodelist. + +The performance characteristics the kernel provides for the local initiators +are exported are as follows:: + + # tree -P "read*|write*" /sys/devices/system/node/nodeY/class0/ + /sys/devices/system/node/nodeY/class0/ + |-- read_bandwidth + |-- read_latency + |-- write_bandwidth + `-- write_latency + +The bandwidth attributes are provided in MiB/second. + +The latency attributes are provided in nanoseconds. + +========== +NUMA Cache +========== + +System memory may be constructed in a hierarchy of elements with various +performance characteristics in order to provide large address space of +slower performing memory side-cached by a smaller higher performing +memory. The system physical addresses that initiators are aware of +is provided by the last memory level in the hierarchy. The system +meanwhile uses higher performing memory to transparently cache access +to progressively slower levels. + +The term "far memory" is used to denote the last level memory in the +hierarchy. Each increasing cache level provides higher performing +initiator access, and the term "near memory" represents the fastest +cache provided by the system. + +This numbering is different than CPU caches where the cache level (ex: +L1, L2, L3) uses a CPU centric view with each increased level is lower +performing. In contrast, the memory cache level is centric to the last +level memory, so the higher numbered cache level denotes memory nearer +to the CPU, and further from far memory. + +The memory side caches are not directly addressable by software. When +software accesses a system address, the system will return it from the +near memory cache if it is present. If it is not present, the system +accesses the next level of memory until there is either a hit in that +cache level, or it reaches far memory. + +An application does not need to know about caching attributes in order +to use the system. Software may optionally query the memory cache +attributes in order to maximize the performance out of such a setup. +If the system provides a way for the kernel to discover this information, +for example with ACPI HMAT (Heterogeneous Memory Attribute Table), +the kernel will append these attributes to the NUMA node memory target. + +When the kernel first registers a memory cache with a node, the kernel +will create the following directory:: + + /sys/devices/system/node/nodeX/side_cache/ + +If that directory is not present, the system either does not not provide +a memory side cache, or that information is not accessible to the kernel. + +The attributes for each level of cache is provided under its cache +level index:: + + /sys/devices/system/node/nodeX/side_cache/indexA/ + /sys/devices/system/node/nodeX/side_cache/indexB/ + /sys/devices/system/node/nodeX/side_cache/indexC/ + +Each cache level's directory provides its attributes. For example, the +following shows a single cache level and the attributes available for +software to query:: + + # tree sys/devices/system/node/node0/side_cache/ + /sys/devices/system/node/node0/side_cache/ + |-- index1 + | |-- associativity + | |-- level + | |-- line_size + | |-- size + | `-- write_policy + +The "associativity" will be 0 if it is a direct-mapped cache, and non-zero +for any other indexed based, multi-way associativity. + +The "level" is the distance from the far memory, and matches the number +appended to its "index" directory. + +The "line_size" is the number of bytes accessed on a cache miss. + +The "size" is the number of bytes provided by this cache level. + +The "write_policy" will be 0 for write-back, and non-zero for +write-through caching. + +======== +See Also +======== +.. [1] https://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdf + Section 5.2.27 -- 2.14.4