YARN-11195. Adding document to enable numa (#4501)
Contributed by Samrat Deb.
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<!---
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License. See accompanying LICENSE file.
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-->
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# NUMA
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Non-uniform memory access (NUMA) is a computer memory design used in multiprocessing,
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where the memory access time depends on the memory location relative to the processor.
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Under NUMA, a processor can access its own local memory faster than non-local memory
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(memory local to another processor or memory shared between processors).
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Yarn Containers can make benefit of this NUMA design to get better performance by binding to a
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specific NUMA node and all subsequent memory allocations will be served by the same node,
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reducing remote memory accesses. NUMA support for YARN Container has to be enabled only if worker
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node machines has NUMA support.
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# Enabling NUMA
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### Prerequisites
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- As of now, NUMA awareness works only with `LinuxContainerExecutor` (LCE)
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- To use the feature of NUMA awareness in the cluster,It must be enabled with
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LinuxContainerExecutor (LCE)
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- Steps to enable SecureContainer (LCE) for cluster is documented [here](SecureContainer.md)
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## Configurations
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**1) Enable/Disable the NUMA awareness**
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This property enables the NUMA awareness feature in the Node Manager
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for the containers. By default, the value of this property is false which means it is disabled.
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If this property is `true` then only the below configurations will be applicable otherwise they
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will be ignored.
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In `yarn-site.xml` add
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```
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<property>
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<name>yarn.nodemanager.numa-awareness.enabled</name>
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<value>true</value>
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</property>
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```
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**2) NUMA topology**
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This property decides whether to read the NUMA topology from the system or from the
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configurations. If this property value is true then the topology will be read from the system using
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`numactl --hardware` command in UNIX systems and similar way in windows.
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If this property is false then the topology will be read using the below configurations.
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Default value of this configuration is false which means NodeManager will read the NUMA topology
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from the below configurations.
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In `yarn-site.xml` add
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```
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<property>
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<name>yarn.nodemanager.numa-awareness.read-topology</name>
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<value>false</value>
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</property>
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```
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**3) Numa command**
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This property is passed when `yarn.nodemanager.numa-awareness.read-topology` is set to true.
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It is recommended to verify the installation of `numactl` command in the Linux OS of every node.
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Use `/usr/bin/numactl --hardware` to verify.
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Sample output of `/usr/bin/numactl --hardware`
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```
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available: 2 nodes (0-1)
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node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
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node 0 size: 191297 MB
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node 0 free: 186539 MB
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node 1 cpus: 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
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node 1 size: 191383 MB
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node 1 free: 185914 MB
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node distances:
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node 0 1
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0: 10 21
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1: 21 10
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```
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In `yarn-site.xml` add
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```
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<property>
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<name>yarn.nodemanager.numa-awareness.numactl.cmd</name>
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<value>/usr/bin/numactl</value>
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</property>
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```
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**4) NUMA nodes id’s**
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This property is used to provide the NUMA node ids as comma separated values.It will be read only
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when the `yarn.nodemanager.numa-awareness.read-topology` is false.
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In ```yarn-site.xml``` add
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```
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<property>
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<name>yarn.nodemanager.numa-awareness.node-ids</name>
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<value>0,1</value>
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</property>
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```
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**5) NUMA Node memory**
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This property will be used to read the memory(in MB) configured for each NUMA node specified in
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`yarn.nodemanager.numa-awareness.node-ids` by substituting the node id in the place of
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`<NODE_ID>`.It will be read only when the `yarn.nodemanager.numa-awareness.read-topology`
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is false.
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In `yarn-site.xml` add
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```
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<property>
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<name>yarn.nodemanager.numa-awareness.<NODE_ID>.memory</name>
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<value>191297</value>
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</property>
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```
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The value passed is the per node memory available , from the above sample output of
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`numactl --hardware` the value passed for the property is the memory available i.e `191297`
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**6) NUMA Node CPUs**
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This property will be used to read the number of CPUs configured for each node specified in
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`yarn.nodemanager.numa-awareness.node-ids` by substituting the node id in the place of
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`<NODE_ID>`.It will be read only when the `yarn.nodemanager.numa-awareness.read-topology` is false.
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In ```yarn-site.xml``` add
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```
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<property>
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<name>yarn.nodemanager.numa-awareness.<NODE_ID>.cpus</name>
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<value>48</value>
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</property>
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```
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referring to the `numactl --hardware` output , number of cpu's in a node is `48`.
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**7) Passing java_opts for map/reduce**
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Every container has to be aware of NUMA and the JVM can be notified via passing NUMA flag.
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Spark, Tez and other YARN Applications also need to set the container JVM Opts to leverage
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NUMA Support.
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In ```mapred-site.xml``` add
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```
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<property>
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<name>mapreduce.reduce.java.opts</name>
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<value>-XX:+UseNUMA</value>
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</property>
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<property>
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<name>mapreduce.map.java.opts</name>
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<value>-XX:+UseNUMA</value>
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</property>
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```
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# Default configuration
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| Property | Default value |
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| --- |-----|
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|yarn.nodemanager.numa-awareness.enabled|false|
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|yarn.nodemanager.numa-awareness.read-topology|false|
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# Enable numa balancing at OS Level (Optional)
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In linux, by default numa balancing is by default off. For more performance improvement,
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NumaBalancing can be turned on for all the nodes in cluster
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```
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echo 1 | sudo tee /proc/sys/kernel/numa_balancing
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```
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# Verify
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**1) NodeManager log**
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In any of the NodeManager, grep log file using below command
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`grep "NUMA resources allocation is enabled," *`
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Sample log with `LinuxContainerExecutor` enabled message
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```
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<nodemanager_ip>.log.2022-06-24-19.gz:2022-06-24 19:16:40,178 INFO org.apache.hadoop.yarn.server.nodemanager.containermanager.linux.resources.numa.NumaResourceHandlerImpl (main): NUMA resources allocation is enabled, initializing NUMA resources allocator.
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```
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**2) Container Log**
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Grep the NodeManager log using below grep command to check if a container is assigned with NUMA node
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resources.
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`grep "NUMA node" | grep <container_id>`
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