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[134.134.136.126]) by mx.google.com with ESMTPS id j17si2724426pfn.271.2019.02.14.09.10.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 Feb 2019 09:10:45 -0800 (PST) Received-SPF: pass (google.com: domain of keith.busch@intel.com designates 134.134.136.126 as permitted sender) client-ip=134.134.136.126; Authentication-Results: mx.google.com; spf=pass (google.com: domain of keith.busch@intel.com designates 134.134.136.126 as permitted sender) smtp.mailfrom=keith.busch@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Feb 2019 09:10:44 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,369,1544515200"; d="scan'208";a="133613144" Received: from unknown (HELO localhost.lm.intel.com) ([10.232.112.69]) by FMSMGA003.fm.intel.com with ESMTP; 14 Feb 2019 09:10:44 -0800 From: Keith Busch To: linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org Cc: Greg Kroah-Hartman , Rafael Wysocki , Dave Hansen , Dan Williams , Keith Busch Subject: [PATCHv6 10/10] doc/mm: New documentation for memory performance Date: Thu, 14 Feb 2019 10:10:17 -0700 Message-Id: <20190214171017.9362-11-keith.busch@intel.com> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20190214171017.9362-1-keith.busch@intel.com> References: <20190214171017.9362-1-keith.busch@intel.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP 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. Reviewed-by: Mike Rapoport Signed-off-by: Keith Busch --- Documentation/admin-guide/mm/numaperf.rst | 164 ++++++++++++++++++++++++++++++ 1 file changed, 164 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..be8a23bb075d --- /dev/null +++ b/Documentation/admin-guide/mm/numaperf.rst @@ -0,0 +1,164 @@ +.. _numaperf: + +============= +NUMA Locality +============= + +Some platforms may have multiple types of memory attached to a compute +node. These disparate memory ranges may 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 supports such heterogeneous memory by grouping each memory type +under different domains, or "nodes", based on 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 local to one or more compute nodes relative to +other nodes. The following diagram shows one such example of two compute +nodes 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 physical address +ranges accessible 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 provides symlinks to each other. The following example lists the +relationship for the access class "0" memory initiators and targets, which is +the of nodes with the highest performing access relationship:: + + # symlinks -v /sys/devices/system/node/nodeX/access0/targets/ + relative: /sys/devices/system/node/nodeX/access0/targets/nodeY -> ../../nodeY + + # symlinks -v /sys/devices/system/node/nodeY/access0/initiators/ + relative: /sys/devices/system/node/nodeY/access0/initiators/nodeX -> ../../nodeX + +================ +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 access class 0 initiators as follows:: + + /sys/devices/system/node/nodeY/access0/initiators/ + +These attributes apply only when accessed from nodes that have the +are linked under the this access's inititiators. + +The performance characteristics the kernel provides for the local initiators +are exported are as follows:: + + # tree -P "read*|write*" /sys/devices/system/node/nodeY/access0/initiators/ + /sys/devices/system/node/nodeY/access0/initiators/ + |-- read_bandwidth + |-- read_latency + |-- write_bandwidth + `-- write_latency + +The bandwidth attributes are provided in MiB/second. + +The latency attributes are provided in nanoseconds. + +The values reported here correspond to the rated latency and bandwidth +for the platform. + +========== +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 cached by a smaller higher performing memory. The +system physical addresses memory initiators are aware of are 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-side view where 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/memory_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/memory_side_cache/indexA/ + /sys/devices/system/node/nodeX/memory_side_cache/indexB/ + /sys/devices/system/node/nodeX/memory_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/memory_side_cache/ + /sys/devices/system/node/node0/memory_side_cache/ + |-- index1 + | |-- associativity + | |-- 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 "line_size" is the number of bytes accessed from the next cache +level on a 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