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Chapter 14. Performance Addon Operator for low latency nodes
14.1. Understanding low latency
The emergence of Edge computing in the area of Telco / 5G plays a key role in reducing latency and congestion problems and improving application performance.
Simply put, latency determines how fast data (packets) moves from the sender to receiver and returns to the sender after processing by the receiver. Obviously, maintaining a network architecture with the lowest possible delay of latency speeds is key for meeting the network performance requirements of 5G. Compared to 4G technology, with an average latency of 50ms, 5G is targeted to reach latency numbers of 1ms or less. This reduction in latency boosts wireless throughput by a factor of 10.
Many of the deployed applications in the Telco space require low latency that can only tolerate zero packet loss. Tuning for zero packet loss helps mitigate the inherent issues that degrade network performance. For more information, see Tuning for Zero Packet Loss in Red Hat OpenStack Platform (RHOSP).
The Edge computing initiative also comes in to play for reducing latency rates. Think of it as literally being on the edge of the cloud and closer to the user. This greatly reduces the distance between the user and distant data centers, resulting in reduced application response times and performance latency.
Administrators must be able to manage their many Edge sites and local services in a centralized way so that all of the deployments can run at the lowest possible management cost. They also need an easy way to deploy and configure certain nodes of their cluster for real-time low latency and high-performance purposes. Low latency nodes are useful for applications such as Cloud-native Network Functions (CNF) and Data Plane Development Kit (DPDK).
OpenShift Container Platform currently provides mechanisms to tune software on an OpenShift Container Platform cluster for real-time running and low latency (around <20 microseconds reaction time). This includes tuning the kernel and OpenShift Container Platform set values, installing a kernel, and reconfiguring the machine. But this method requires setting up four different Operators and performing many configurations that, when done manually, is complex and could be prone to mistakes.
OpenShift Container Platform provides a Performance Addon Operator to implement automatic tuning to achieve low latency performance for OpenShift applications. The cluster administrator uses this performance profile configuration that makes it easier to make these changes in a more reliable way. The administrator can specify whether to update the kernel to kernel-rt, reserve CPUs for cluster and operating system housekeeping duties, including pod infra containers, and isolate CPUs for application containers to run the workloads.
14.1.1. About hyperthreading for low latency and real-time applications
Hyperthreading is an Intel processor technology that allows a physical CPU processor core to function as two logical cores, executing two independent threads simultaneously. Hyperthreading allows for better system throughput for certain workload types where parallel processing is beneficial. The default OpenShift Container Platform configuration expects hyperthreading to be enabled by default.
For telecommunications applications, it is important to design your application infrastructure to minimize latency as much as possible. Hyperthreading can slow performance times and negatively affect throughput for compute intensive workloads that require low latency. Disabling hyperthreading ensures predictable performance and can decrease processing times for these workloads.
Hyperthreading implementation and configuration differs depending on the hardware you are running OpenShift Container Platform on. Consult the relevant host hardware tuning information for more details of the hyperthreading implementation specific to that hardware. Disabling hyperthreading can increase the cost per core of the cluster.
Additional resources
14.2. Installing the Performance Addon Operator
Performance Addon Operator provides the ability to enable advanced node performance tunings on a set of nodes. As a cluster administrator, you can install Performance Addon Operator using the OpenShift Container Platform CLI or the web console.
14.2.1. Installing the Operator using the CLI
As a cluster administrator, you can install the Operator using the CLI.
Prerequisites
- A cluster installed on bare-metal hardware.
-
Install the OpenShift CLI (
oc
). -
Log in as a user with
cluster-admin
privileges.
Procedure
Create a namespace for the Performance Addon Operator by completing the following actions:
Create the following Namespace Custom Resource (CR) that defines the
openshift-performance-addon-operator
namespace, and then save the YAML in thepao-namespace.yaml
file:apiVersion: v1 kind: Namespace metadata: name: openshift-performance-addon-operator annotations: workload.openshift.io/allowed: management
Create the namespace by running the following command:
$ oc create -f pao-namespace.yaml
Install the Performance Addon Operator in the namespace you created in the previous step by creating the following objects:
Create the following
OperatorGroup
CR and save the YAML in thepao-operatorgroup.yaml
file:apiVersion: operators.coreos.com/v1 kind: OperatorGroup metadata: name: openshift-performance-addon-operator namespace: openshift-performance-addon-operator
Create the
OperatorGroup
CR by running the following command:$ oc create -f pao-operatorgroup.yaml
Run the following command to get the
channel
value required for the next step.$ oc get packagemanifest performance-addon-operator -n openshift-marketplace -o jsonpath='{.status.defaultChannel}'
Example output
4.10
Create the following Subscription CR and save the YAML in the
pao-sub.yaml
file:Example Subscription
apiVersion: operators.coreos.com/v1alpha1 kind: Subscription metadata: name: openshift-performance-addon-operator-subscription namespace: openshift-performance-addon-operator spec: channel: "<channel>" 1 name: performance-addon-operator source: redhat-operators 2 sourceNamespace: openshift-marketplace
Create the Subscription object by running the following command:
$ oc create -f pao-sub.yaml
Change to the
openshift-performance-addon-operator
project:$ oc project openshift-performance-addon-operator
14.2.2. Installing the Performance Addon Operator using the web console
As a cluster administrator, you can install the Performance Addon Operator using the web console.
You must create the Namespace
CR and OperatorGroup
CR as mentioned in the previous section.
Procedure
Install the Performance Addon Operator using the OpenShift Container Platform web console:
-
In the OpenShift Container Platform web console, click Operators
OperatorHub. - Choose Performance Addon Operator from the list of available Operators, and then click Install.
- On the Install Operator page, select All namespaces on the cluster. Then, click Install.
-
In the OpenShift Container Platform web console, click Operators
Optional: Verify that the performance-addon-operator installed successfully:
-
Switch to the Operators
Installed Operators page. Ensure that Performance Addon Operator is listed in the openshift-operators project with a Status of Succeeded.
NoteDuring installation an Operator might display a Failed status. If the installation later succeeds with a Succeeded message, you can ignore the Failed message.
If the Operator does not appear as installed, you can troubleshoot further:
-
Go to the Operators
Installed Operators page and inspect the Operator Subscriptions and Install Plans tabs for any failure or errors under Status. -
Go to the Workloads
Pods page and check the logs for pods in the openshift-operators
project.
-
Go to the Operators
-
Switch to the Operators
14.3. Upgrading Performance Addon Operator
You can manually upgrade to the next minor version of Performance Addon Operator and monitor the status of an update by using the web console.
14.3.1. About upgrading Performance Addon Operator
- You can upgrade to the next minor version of Performance Addon Operator by using the OpenShift Container Platform web console to change the channel of your Operator subscription.
- You can enable automatic z-stream updates during Performance Addon Operator installation.
- Updates are delivered via the Marketplace Operator, which is deployed during OpenShift Container Platform installation.The Marketplace Operator makes external Operators available to your cluster.
- The amount of time an update takes to complete depends on your network connection. Most automatic updates complete within fifteen minutes.
14.3.1.1. How Performance Addon Operator upgrades affect your cluster
- Neither the low latency tuning nor huge pages are affected.
- Updating the Operator should not cause any unexpected reboots.
14.3.1.2. Upgrading Performance Addon Operator to the next minor version
You can manually upgrade Performance Addon Operator to the next minor version by using the OpenShift Container Platform web console to change the channel of your Operator subscription.
Prerequisites
- Access to the cluster as a user with the cluster-admin role.
Procedure
-
Access the web console and navigate to Operators
Installed Operators. - Click Performance Addon Operator to open the Operator details page.
- Click the Subscription tab to open the Subscription details page.
- In the Update channel pane, click the pencil icon on the right side of the version number to open the Change Subscription update channel window.
- Select the next minor version. For example, if you want to upgrade to Performance Addon Operator 4.10, select 4.10.
- Click Save.
Check the status of the upgrade by navigating to Operators
Installed Operators. You can also check the status by running the following oc
command:$ oc get csv -n openshift-performance-addon-operator
14.3.1.3. Upgrading Performance Addon Operator when previously installed to a specific namespace
If you previously installed the Performance Addon Operator to a specific namespace on the cluster, for example openshift-performance-addon-operator
, modify the OperatorGroup
object to remove the targetNamespaces
entry before upgrading.
Prerequisites
- Install the OpenShift Container Platform CLI (oc).
- Log in to the OpenShift cluster as a user with cluster-admin privileges.
Procedure
Edit the Performance Addon Operator
OperatorGroup
CR and remove thespec
element that contains thetargetNamespaces
entry by running the following command:$ oc patch operatorgroup -n openshift-performance-addon-operator openshift-performance-addon-operator --type json -p '[{ "op": "remove", "path": "/spec" }]'
- Wait until the Operator Lifecycle Manager (OLM) processes the change.
Verify that the OperatorGroup CR change has been successfully applied. Check that the
OperatorGroup
CRspec
element has been removed:$ oc describe -n openshift-performance-addon-operator og openshift-performance-addon-operator
- Proceed with the Performance Addon Operator upgrade.
14.3.2. Monitoring upgrade status
The best way to monitor Performance Addon Operator upgrade status is to watch the ClusterServiceVersion
(CSV) PHASE
. You can also monitor the CSV conditions in the web console or by running the oc get csv
command.
The PHASE
and conditions values are approximations that are based on available information.
Prerequisites
-
Access to the cluster as a user with the
cluster-admin
role. -
Install the OpenShift CLI (
oc
).
Procedure
Run the following command:
$ oc get csv
Review the output, checking the
PHASE
field. For example:VERSION REPLACES PHASE 4.10.0 performance-addon-operator.v4.10.0 Installing 4.8.0 Replacing
Run
get csv
again to verify the output:# oc get csv
Example output
NAME DISPLAY VERSION REPLACES PHASE performance-addon-operator.v4.10.0 Performance Addon Operator 4.10.0 performance-addon-operator.v4.8.0 Succeeded
14.4. Provisioning real-time and low latency workloads
Many industries and organizations need extremely high performance computing and might require low and predictable latency, especially in the financial and telecommunications industries. For these industries, with their unique requirements, OpenShift Container Platform provides a Performance Addon Operator to implement automatic tuning to achieve low latency performance and consistent response time for OpenShift Container Platform applications.
The cluster administrator can use this performance profile configuration to make these changes in a more reliable way. The administrator can specify whether to update the kernel to kernel-rt (real-time), reserve CPUs for cluster and operating system housekeeping duties, including pod infra containers, and isolate CPUs for application containers to run the workloads.
The usage of execution probes in conjunction with applications that require guaranteed CPUs can cause latency spikes. It is recommended to use other probes, such as a properly configured set of network probes, as an alternative.
14.4.1. Known limitations for real-time
In most deployments, kernel-rt is supported only on worker nodes when you use a standard cluster with three control plane nodes and three worker nodes. There are exceptions for compact and single nodes on OpenShift Container Platform deployments. For installations on a single node, kernel-rt is supported on the single control plane node.
To fully utilize the real-time mode, the containers must run with elevated privileges. See Set capabilities for a Container for information on granting privileges.
OpenShift Container Platform restricts the allowed capabilities, so you might need to create a SecurityContext
as well.
This procedure is fully supported with bare metal installations using Red Hat Enterprise Linux CoreOS (RHCOS) systems.
Establishing the right performance expectations refers to the fact that the real-time kernel is not a panacea. Its objective is consistent, low-latency determinism offering predictable response times. There is some additional kernel overhead associated with the real-time kernel. This is due primarily to handling hardware interruptions in separately scheduled threads. The increased overhead in some workloads results in some degradation in overall throughput. The exact amount of degradation is very workload dependent, ranging from 0% to 30%. However, it is the cost of determinism.
14.4.2. Provisioning a worker with real-time capabilities
- Install Performance Addon Operator to the cluster.
- Optional: Add a node to the OpenShift Container Platform cluster. See Setting BIOS parameters.
-
Add the label
worker-rt
to the worker nodes that require the real-time capability by using theoc
command. Create a new machine config pool for real-time nodes:
apiVersion: machineconfiguration.openshift.io/v1 kind: MachineConfigPool metadata: name: worker-rt labels: machineconfiguration.openshift.io/role: worker-rt spec: machineConfigSelector: matchExpressions: - { key: machineconfiguration.openshift.io/role, operator: In, values: [worker, worker-rt], } paused: false nodeSelector: matchLabels: node-role.kubernetes.io/worker-rt: ""
Note that a machine config pool worker-rt is created for group of nodes that have the label
worker-rt
.Add the node to the proper machine config pool by using node role labels.
NoteYou must decide which nodes are configured with real-time workloads. You could configure all of the nodes in the cluster, or a subset of the nodes. The Performance Addon Operator that expects all of the nodes are part of a dedicated machine config pool. If you use all of the nodes, you must point the Performance Addon Operator to the worker node role label. If you use a subset, you must group the nodes into a new machine config pool.
-
Create the
PerformanceProfile
with the proper set of housekeeping cores andrealTimeKernel: enabled: true
. You must set
machineConfigPoolSelector
inPerformanceProfile
:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: example-performanceprofile spec: ... realTimeKernel: enabled: true nodeSelector: node-role.kubernetes.io/worker-rt: "" machineConfigPoolSelector: machineconfiguration.openshift.io/role: worker-rt
Verify that a matching machine config pool exists with a label:
$ oc describe mcp/worker-rt
Example output
Name: worker-rt Namespace: Labels: machineconfiguration.openshift.io/role=worker-rt
- OpenShift Container Platform will start configuring the nodes, which might involve multiple reboots. Wait for the nodes to settle. This can take a long time depending on the specific hardware you use, but 20 minutes per node is expected.
- Verify everything is working as expected.
14.4.3. Verifying the real-time kernel installation
Use this command to verify that the real-time kernel is installed:
$ oc get node -o wide
Note the worker with the role worker-rt
that contains the string 4.18.0-305.30.1.rt7.102.el8_4.x86_64 cri-o://1.23.0-99.rhaos4.10.gitc3131de.el8
:
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME rt-worker-0.example.com Ready worker,worker-rt 5d17h v1.23.0 128.66.135.107 <none> Red Hat Enterprise Linux CoreOS 46.82.202008252340-0 (Ootpa) 4.18.0-305.30.1.rt7.102.el8_4.x86_64 cri-o://1.23.0-99.rhaos4.10.gitc3131de.el8 [...]
14.4.4. Creating a workload that works in real-time
Use the following procedures for preparing a workload that will use real-time capabilities.
Procedure
-
Create a pod with a QoS class of
Guaranteed
. - Optional: Disable CPU load balancing for DPDK.
- Assign a proper node selector.
When writing your applications, follow the general recommendations described in Application tuning and deployment.
14.4.5. Creating a pod with a QoS class of Guaranteed
Keep the following in mind when you create a pod that is given a QoS class of Guaranteed
:
- Every container in the pod must have a memory limit and a memory request, and they must be the same.
- Every container in the pod must have a CPU limit and a CPU request, and they must be the same.
The following example shows the configuration file for a pod that has one container. The container has a memory limit and a memory request, both equal to 200 MiB. The container has a CPU limit and a CPU request, both equal to 1 CPU.
apiVersion: v1 kind: Pod metadata: name: qos-demo namespace: qos-example spec: containers: - name: qos-demo-ctr image: <image-pull-spec> resources: limits: memory: "200Mi" cpu: "1" requests: memory: "200Mi" cpu: "1"
Create the pod:
$ oc apply -f qos-pod.yaml --namespace=qos-example
View detailed information about the pod:
$ oc get pod qos-demo --namespace=qos-example --output=yaml
Example output
spec: containers: ... status: qosClass: Guaranteed
NoteIf a container specifies its own memory limit, but does not specify a memory request, OpenShift Container Platform automatically assigns a memory request that matches the limit. Similarly, if a container specifies its own CPU limit, but does not specify a CPU request, OpenShift Container Platform automatically assigns a CPU request that matches the limit.
14.4.6. Optional: Disabling CPU load balancing for DPDK
Functionality to disable or enable CPU load balancing is implemented on the CRI-O level. The code under the CRI-O disables or enables CPU load balancing only when the following requirements are met.
The pod must use the
performance-<profile-name>
runtime class. You can get the proper name by looking at the status of the performance profile, as shown here:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile ... status: ... runtimeClass: performance-manual
-
The pod must have the
cpu-load-balancing.crio.io: true
annotation.
The Performance Addon Operator is responsible for the creation of the high-performance runtime handler config snippet under relevant nodes and for creation of the high-performance runtime class under the cluster. It will have the same content as default runtime handler except it enables the CPU load balancing configuration functionality.
To disable the CPU load balancing for the pod, the Pod
specification must include the following fields:
apiVersion: v1 kind: Pod metadata: ... annotations: ... cpu-load-balancing.crio.io: "disable" ... ... spec: ... runtimeClassName: performance-<profile_name> ...
Only disable CPU load balancing when the CPU manager static policy is enabled and for pods with guaranteed QoS that use whole CPUs. Otherwise, disabling CPU load balancing can affect the performance of other containers in the cluster.
14.4.7. Assigning a proper node selector
The preferred way to assign a pod to nodes is to use the same node selector the performance profile used, as shown here:
apiVersion: v1 kind: Pod metadata: name: example spec: # ... nodeSelector: node-role.kubernetes.io/worker-rt: ""
For more information, see Placing pods on specific nodes using node selectors.
14.4.8. Scheduling a workload onto a worker with real-time capabilities
Use label selectors that match the nodes attached to the machine config pool that was configured for low latency by the Performance Addon Operator. For more information, see Assigning pods to nodes.
14.4.9. Managing device interrupt processing for guaranteed pod isolated CPUs
The Performance Addon Operator can manage host CPUs by dividing them into reserved CPUs for cluster and operating system housekeeping duties, including pod infra containers, and isolated CPUs for application containers to run the workloads. This allows you to set CPUs for low latency workloads as isolated.
Device interrupts are load balanced between all isolated and reserved CPUs to avoid CPUs being overloaded, with the exception of CPUs where there is a guaranteed pod running. Guaranteed pod CPUs are prevented from processing device interrupts when the relevant annotations are set for the pod.
In the performance profile, globallyDisableIrqLoadBalancing
is used to manage whether device interrupts are processed or not. For certain workloads the reserved CPUs are not always sufficient for dealing with device interrupts, and for this reason, device interrupts are not globally disabled on the isolated CPUs. By default, Performance Addon Operator does not disable device interrupts on isolated CPUs.
To achieve low latency for workloads, some (but not all) pods require the CPUs they are running on to not process device interrupts. A pod annotation, irq-load-balancing.crio.io
, is used to define whether device interrupts are processed or not. When configured, CRI-O disables device interrupts only as long as the pod is running.
14.4.9.1. Disabling CPU CFS quota
To reduce CPU throttling for individual guaranteed pods, create a pod specification with the annotation cpu-quota.crio.io: "disable"
. This annotation disables the CPU completely fair scheduler (CFS) quota at the pod run time. The following pod specification contains this annotation:
apiVersion: performance.openshift.io/v2 kind: Pod metadata: annotations: cpu-quota.crio.io: "disable" spec: runtimeClassName: performance-<profile_name> ...
Only disable CPU CFS quota when the CPU manager static policy is enabled and for pods with guaranteed QoS that use whole CPUs. Otherwise, disabling CPU CFS quota can affect the performance of other containers in the cluster.
14.4.9.2. Disabling global device interrupts handling in Performance Addon Operator
To configure Performance Addon Operator to disable global device interrupts for the isolated CPU set, set the globallyDisableIrqLoadBalancing
field in the performance profile to true
. When true
, conflicting pod annotations are ignored. When false
, IRQ loads are balanced across all CPUs.
A performance profile snippet illustrates this setting:
apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: manual spec: globallyDisableIrqLoadBalancing: true ...
14.4.9.3. Disabling interrupt processing for individual pods
To disable interrupt processing for individual pods, ensure that globallyDisableIrqLoadBalancing
is set to false
in the performance profile. Then, in the pod specification, set the irq-load-balancing.crio.io
pod annotation to disable
. The following pod specification contains this annotation:
apiVersion: performance.openshift.io/v2 kind: Pod metadata: annotations: irq-load-balancing.crio.io: "disable" spec: runtimeClassName: performance-<profile_name> ...
14.4.10. Upgrading the performance profile to use device interrupt processing
When you upgrade the Performance Addon Operator performance profile custom resource definition (CRD) from v1 or v1alpha1 to v2, globallyDisableIrqLoadBalancing
is set to true
on existing profiles.
globallyDisableIrqLoadBalancing
toggles whether IRQ load balancing will be disabled for the Isolated CPU set. When the option is set to true
it disables IRQ load balancing for the Isolated CPU set. Setting the option to false
allows the IRQs to be balanced across all CPUs.
14.4.10.1. Supported API Versions
The Performance Addon Operator supports v2
, v1
, and v1alpha1
for the performance profile apiVersion
field. The v1 and v1alpha1 APIs are identical. The v2 API includes an optional boolean field globallyDisableIrqLoadBalancing
with a default value of false
.
14.4.10.1.1. Upgrading Performance Addon Operator API from v1alpha1 to v1
When upgrading Performance Addon Operator API version from v1alpha1 to v1, the v1alpha1 performance profiles are converted on-the-fly using a "None" Conversion strategy and served to the Performance Addon Operator with API version v1.
14.4.10.1.2. Upgrading Performance Addon Operator API from v1alpha1 or v1 to v2
When upgrading from an older Performance Addon Operator API version, the existing v1 and v1alpha1 performance profiles are converted using a conversion webhook that injects the globallyDisableIrqLoadBalancing
field with a value of true
.
14.4.11. Configuring a node for IRQ dynamic load balancing
To configure a cluster node to handle IRQ dynamic load balancing, do the following:
- Log in to the OpenShift Container Platform cluster as a user with cluster-admin privileges.
-
Set the performance profile
apiVersion
to useperformance.openshift.io/v2
. -
Remove the
globallyDisableIrqLoadBalancing
field or set it tofalse
. Set the appropriate isolated and reserved CPUs. The following snippet illustrates a profile that reserves 2 CPUs. IRQ load-balancing is enabled for pods running on the
isolated
CPU set:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: dynamic-irq-profile spec: cpu: isolated: 2-5 reserved: 0-1 ...
NoteWhen you configure reserved and isolated CPUs, the infra containers in pods use the reserved CPUs and the application containers use the isolated CPUs.
Create the pod that uses exclusive CPUs, and set
irq-load-balancing.crio.io
andcpu-quota.crio.io
annotations todisable
. For example:apiVersion: v1 kind: Pod metadata: name: dynamic-irq-pod annotations: irq-load-balancing.crio.io: "disable" cpu-quota.crio.io: "disable" spec: containers: - name: dynamic-irq-pod image: "registry.redhat.io/openshift4/cnf-tests-rhel8:v4.10" command: ["sleep", "10h"] resources: requests: cpu: 2 memory: "200M" limits: cpu: 2 memory: "200M" nodeSelector: node-role.kubernetes.io/worker-cnf: "" runtimeClassName: performance-dynamic-irq-profile ...
-
Enter the pod
runtimeClassName
in the form performance-<profile_name>, where <profile_name> is thename
from thePerformanceProfile
YAML, in this example,performance-dynamic-irq-profile
. - Set the node selector to target a cnf-worker.
Ensure the pod is running correctly. Status should be
running
, and the correct cnf-worker node should be set:$ oc get pod -o wide
Expected output
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES dynamic-irq-pod 1/1 Running 0 5h33m <ip-address> <node-name> <none> <none>
Get the CPUs that the pod configured for IRQ dynamic load balancing runs on:
$ oc exec -it dynamic-irq-pod -- /bin/bash -c "grep Cpus_allowed_list /proc/self/status | awk '{print $2}'"
Expected output
Cpus_allowed_list: 2-3
Ensure the node configuration is applied correctly. SSH into the node to verify the configuration.
$ oc debug node/<node-name>
Expected output
Starting pod/<node-name>-debug ... To use host binaries, run `chroot /host` Pod IP: <ip-address> If you don't see a command prompt, try pressing enter. sh-4.4#
Verify that you can use the node file system:
sh-4.4# chroot /host
Expected output
sh-4.4#
Ensure the default system CPU affinity mask does not include the
dynamic-irq-pod
CPUs, for example, CPUs 2 and 3.$ cat /proc/irq/default_smp_affinity
Example output
33
Ensure the system IRQs are not configured to run on the
dynamic-irq-pod
CPUs:find /proc/irq/ -name smp_affinity_list -exec sh -c 'i="$1"; mask=$(cat $i); file=$(echo $i); echo $file: $mask' _ {} \;
Example output
/proc/irq/0/smp_affinity_list: 0-5 /proc/irq/1/smp_affinity_list: 5 /proc/irq/2/smp_affinity_list: 0-5 /proc/irq/3/smp_affinity_list: 0-5 /proc/irq/4/smp_affinity_list: 0 /proc/irq/5/smp_affinity_list: 0-5 /proc/irq/6/smp_affinity_list: 0-5 /proc/irq/7/smp_affinity_list: 0-5 /proc/irq/8/smp_affinity_list: 4 /proc/irq/9/smp_affinity_list: 4 /proc/irq/10/smp_affinity_list: 0-5 /proc/irq/11/smp_affinity_list: 0 /proc/irq/12/smp_affinity_list: 1 /proc/irq/13/smp_affinity_list: 0-5 /proc/irq/14/smp_affinity_list: 1 /proc/irq/15/smp_affinity_list: 0 /proc/irq/24/smp_affinity_list: 1 /proc/irq/25/smp_affinity_list: 1 /proc/irq/26/smp_affinity_list: 1 /proc/irq/27/smp_affinity_list: 5 /proc/irq/28/smp_affinity_list: 1 /proc/irq/29/smp_affinity_list: 0 /proc/irq/30/smp_affinity_list: 0-5
Some IRQ controllers do not support IRQ re-balancing and will always expose all online CPUs as the IRQ mask. These IRQ controllers effectively run on CPU 0. For more information on the host configuration, SSH into the host and run the following, replacing <irq-num>
with the CPU number that you want to query:
$ cat /proc/irq/<irq-num>/effective_affinity
14.4.12. Configuring hyperthreading for a cluster
To configure hyperthreading for an OpenShift Container Platform cluster, set the CPU threads in the performance profile to the same cores that are configured for the reserved or isolated CPU pools.
If you configure a performance profile, and subsequently change the hyperthreading configuration for the host, ensure that you update the CPU isolated
and reserved
fields in the PerformanceProfile
YAML to match the new configuration.
Disabling a previously enabled host hyperthreading configuration can cause the CPU core IDs listed in the PerformanceProfile
YAML to be incorrect. This incorrect configuration can cause the node to become unavailable because the listed CPUs can no longer be found.
Prerequisites
-
Access to the cluster as a user with the
cluster-admin
role. - Install the OpenShift CLI (oc).
Procedure
Ascertain which threads are running on what CPUs for the host you want to configure.
You can view which threads are running on the host CPUs by logging in to the cluster and running the following command:
$ lscpu --all --extended
Example output
CPU NODE SOCKET CORE L1d:L1i:L2:L3 ONLINE MAXMHZ MINMHZ 0 0 0 0 0:0:0:0 yes 4800.0000 400.0000 1 0 0 1 1:1:1:0 yes 4800.0000 400.0000 2 0 0 2 2:2:2:0 yes 4800.0000 400.0000 3 0 0 3 3:3:3:0 yes 4800.0000 400.0000 4 0 0 0 0:0:0:0 yes 4800.0000 400.0000 5 0 0 1 1:1:1:0 yes 4800.0000 400.0000 6 0 0 2 2:2:2:0 yes 4800.0000 400.0000 7 0 0 3 3:3:3:0 yes 4800.0000 400.0000
In this example, there are eight logical CPU cores running on four physical CPU cores. CPU0 and CPU4 are running on physical Core0, CPU1 and CPU5 are running on physical Core 1, and so on.
Alternatively, to view the threads that are set for a particular physical CPU core (
cpu0
in the example below), open a command prompt and run the following:$ cat /sys/devices/system/cpu/cpu0/topology/thread_siblings_list
Example output
0-4
Apply the isolated and reserved CPUs in the
PerformanceProfile
YAML. For example, you can set logical cores CPU0 and CPU4 asisolated
, and logical cores CPU1 to CPU3 and CPU5 to CPU7 asreserved
. When you configure reserved and isolated CPUs, the infra containers in pods use the reserved CPUs and the application containers use the isolated CPUs.... cpu: isolated: 0,4 reserved: 1-3,5-7 ...
NoteThe reserved and isolated CPU pools must not overlap and together must span all available cores in the worker node.
Hyperthreading is enabled by default on most Intel processors. If you enable hyperthreading, all threads processed by a particular core must be isolated or processed on the same core.
14.4.12.1. Disabling hyperthreading for low latency applications
When configuring clusters for low latency processing, consider whether you want to disable hyperthreading before you deploy the cluster. To disable hyperthreading, do the following:
- Create a performance profile that is appropriate for your hardware and topology.
Set
nosmt
as an additional kernel argument. The following example performance profile illustrates this setting:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: example-performanceprofile spec: additionalKernelArgs: - nmi_watchdog=0 - audit=0 - mce=off - processor.max_cstate=1 - idle=poll - intel_idle.max_cstate=0 - nosmt cpu: isolated: 2-3 reserved: 0-1 hugepages: defaultHugepagesSize: 1G pages: - count: 2 node: 0 size: 1G nodeSelector: node-role.kubernetes.io/performance: '' realTimeKernel: enabled: true
NoteWhen you configure reserved and isolated CPUs, the infra containers in pods use the reserved CPUs and the application containers use the isolated CPUs.
14.5. Tuning nodes for low latency with the performance profile
The performance profile lets you control latency tuning aspects of nodes that belong to a certain machine config pool. After you specify your settings, the PerformanceProfile
object is compiled into multiple objects that perform the actual node level tuning:
-
A
MachineConfig
file that manipulates the nodes. -
A
KubeletConfig
file that configures the Topology Manager, the CPU Manager, and the OpenShift Container Platform nodes. - The Tuned profile that configures the Node Tuning Operator.
You can use a performance profile to specify whether to update the kernel to kernel-rt, to allocate huge pages, and to partition the CPUs for performing housekeeping duties or running workloads.
You can manually create the PerformanceProfile
object or use the Performance Profile Creator (PPC) to generate a performance profile. See the additional resources below for more information on the PPC.
Sample performance profile
apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: performance spec: cpu: isolated: "4-15" 1 reserved: "0-3" 2 hugepages: defaultHugepagesSize: "1G" pages: - size: "1G" count: 16 node: 0 realTimeKernel: enabled: true 3 numa: 4 topologyPolicy: "best-effort" nodeSelector: node-role.kubernetes.io/worker-cnf: "" 5
- 1
- Use this field to isolate specific CPUs to use with application containers for workloads. Set an even number of isolated CPUs to enable the pods to run without errors when hyperthreading is enabled.
- 2
- Use this field to reserve specific CPUs to use with infra containers for housekeeping.
- 3
- Use this field to install the real-time kernel on the node. Valid values are
true
orfalse
. Setting thetrue
value installs the real-time kernel. - 4
- Use this field to configure the topology manager policy. Valid values are
none
(default),best-effort
,restricted
, andsingle-numa-node
. For more information, see Topology Manager Policies. - 5
- Use this field to specify a node selector to apply the performance profile to specific nodes.
Additional resources
- For information on using the Performance Profile Creator (PPC) to generate a performance profile, see Creating a performance profile.
14.5.1. Configuring huge pages
Nodes must pre-allocate huge pages used in an OpenShift Container Platform cluster. Use the Performance Addon Operator to allocate huge pages on a specific node.
OpenShift Container Platform provides a method for creating and allocating huge pages. Performance Addon Operator provides an easier method for doing this using the performance profile.
For example, in the hugepages
pages
section of the performance profile, you can specify multiple blocks of size
, count
, and, optionally, node
:
hugepages:
defaultHugepagesSize: "1G"
pages:
- size: "1G"
count: 4
node: 0 1
- 1
node
is the NUMA node in which the huge pages are allocated. If you omitnode
, the pages are evenly spread across all NUMA nodes.
Wait for the relevant machine config pool status that indicates the update is finished.
These are the only configuration steps you need to do to allocate huge pages.
Verification
To verify the configuration, see the
/proc/meminfo
file on the node:$ oc debug node/ip-10-0-141-105.ec2.internal
# grep -i huge /proc/meminfo
Example output
AnonHugePages: ###### ## ShmemHugePages: 0 kB HugePages_Total: 2 HugePages_Free: 2 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: #### ## Hugetlb: #### ##
Use
oc describe
to report the new size:$ oc describe node worker-0.ocp4poc.example.com | grep -i huge
Example output
hugepages-1g=true hugepages-###: ### hugepages-###: ###
14.5.2. Allocating multiple huge page sizes
You can request huge pages with different sizes under the same container. This allows you to define more complicated pods consisting of containers with different huge page size needs.
For example, you can define sizes 1G
and 2M
and the Performance Addon Operator will configure both sizes on the node, as shown here:
spec: hugepages: defaultHugepagesSize: 1G pages: - count: 1024 node: 0 size: 2M - count: 4 node: 1 size: 1G
14.5.3. Restricting CPUs for infra and application containers
Generic housekeeping and workload tasks use CPUs in a way that may impact latency-sensitive processes. By default, the container runtime uses all online CPUs to run all containers together, which can result in context switches and spikes in latency. Partitioning the CPUs prevents noisy processes from interfering with latency-sensitive processes by separating them from each other. The following table describes how processes run on a CPU after you have tuned the node using the Performance Add-On Operator:
Process type | Details |
---|---|
| Runs on any CPU except where low latency workload is running |
Infrastructure pods | Runs on any CPU except where low latency workload is running |
Interrupts | Redirects to reserved CPUs (optional in OpenShift Container Platform 4.7 and later) |
Kernel processes | Pins to reserved CPUs |
Latency-sensitive workload pods | Pins to a specific set of exclusive CPUs from the isolated pool |
OS processes/systemd services | Pins to reserved CPUs |
The allocatable capacity of cores on a node for pods of all QoS process types, Burstable
, BestEffort
, or Guaranteed
, is equal to the capacity of the isolated pool. The capacity of the reserved pool is removed from the node’s total core capacity for use by the cluster and operating system housekeeping duties.
Example 1
A node features a capacity of 100 cores. Using a performance profile, the cluster administrator allocates 50 cores to the isolated pool and 50 cores to the reserved pool. The cluster administrator assigns 25 cores to QoS Guaranteed
pods and 25 cores for BestEffort
or Burstable
pods. This matches the capacity of the isolated pool.
Example 2
A node features a capacity of 100 cores. Using a performance profile, the cluster administrator allocates 50 cores to the isolated pool and 50 cores to the reserved pool. The cluster administrator assigns 50 cores to QoS Guaranteed
pods and one core for BestEffort
or Burstable
pods. This exceeds the capacity of the isolated pool by one core. Pod scheduling fails because of insufficient CPU capacity.
The exact partitioning pattern to use depends on many factors like hardware, workload characteristics and the expected system load. Some sample use cases are as follows:
- If the latency-sensitive workload uses specific hardware, such as a network interface controller (NIC), ensure that the CPUs in the isolated pool are as close as possible to this hardware. At a minimum, you should place the workload in the same Non-Uniform Memory Access (NUMA) node.
- The reserved pool is used for handling all interrupts. When depending on system networking, allocate a sufficiently-sized reserve pool to handle all the incoming packet interrupts. In 4.10 and later versions, workloads can optionally be labeled as sensitive.
The decision regarding which specific CPUs should be used for reserved and isolated partitions requires detailed analysis and measurements. Factors like NUMA affinity of devices and memory play a role. The selection also depends on the workload architecture and the specific use case.
The reserved and isolated CPU pools must not overlap and together must span all available cores in the worker node.
To ensure that housekeeping tasks and workloads do not interfere with each other, specify two groups of CPUs in the spec
section of the performance profile.
-
isolated
- Specifies the CPUs for the application container workloads. These CPUs have the lowest latency. Processes in this group have no interruptions and can, for example, reach much higher DPDK zero packet loss bandwidth. -
reserved
- Specifies the CPUs for the cluster and operating system housekeeping duties. Threads in thereserved
group are often busy. Do not run latency-sensitive applications in thereserved
group. Latency-sensitive applications run in theisolated
group.
Procedure
- Create a performance profile appropriate for the environment’s hardware and topology.
Add the
reserved
andisolated
parameters with the CPUs you want reserved and isolated for the infra and application containers:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: infra-cpus spec: cpu: reserved: "0-4,9" 1 isolated: "5-8" 2 nodeSelector: 3 node-role.kubernetes.io/worker: ""
14.6. Reducing NIC queues using the Performance Addon Operator
The Performance Addon Operator allows you to adjust the network interface controller (NIC) queue count for each network device by configuring the performance profile. Device network queues allows the distribution of packets among different physical queues and each queue gets a separate thread for packet processing.
In real-time or low latency systems, all the unnecessary interrupt request lines (IRQs) pinned to the isolated CPUs must be moved to reserved or housekeeping CPUs.
In deployments with applications that require system, OpenShift Container Platform networking or in mixed deployments with Data Plane Development Kit (DPDK) workloads, multiple queues are needed to achieve good throughput and the number of NIC queues should be adjusted or remain unchanged. For example, to achieve low latency the number of NIC queues for DPDK based workloads should be reduced to just the number of reserved or housekeeping CPUs.
Too many queues are created by default for each CPU and these do not fit into the interrupt tables for housekeeping CPUs when tuning for low latency. Reducing the number of queues makes proper tuning possible. Smaller number of queues means a smaller number of interrupts that then fit in the IRQ table.
14.6.1. Adjusting the NIC queues with the performance profile
The performance profile lets you adjust the queue count for each network device.
Supported network devices:
- Non-virtual network devices
- Network devices that support multiple queues (channels)
Unsupported network devices:
- Pure software network interfaces
- Block devices
- Intel DPDK virtual functions
Prerequisites
-
Access to the cluster as a user with the
cluster-admin
role. -
Install the OpenShift CLI (
oc
).
Procedure
-
Log in to the OpenShift Container Platform cluster running the Performance Addon Operator as a user with
cluster-admin
privileges. - Create and apply a performance profile appropriate for your hardware and topology. For guidance on creating a profile, see the "Creating a performance profile" section.
Edit this created performance profile:
$ oc edit -f <your_profile_name>.yaml
Populate the
spec
field with thenet
object. The object list can contain two fields:-
userLevelNetworking
is a required field specified as a boolean flag. IfuserLevelNetworking
istrue
, the queue count is set to the reserved CPU count for all supported devices. The default isfalse
. devices
is an optional field specifying a list of devices that will have the queues set to the reserved CPU count. If the device list is empty, the configuration applies to all network devices. The configuration is as follows:interfaceName
: This field specifies the interface name, and it supports shell-style wildcards, which can be positive or negative.-
Example wildcard syntax is as follows:
<string> .*
-
Negative rules are prefixed with an exclamation mark. To apply the net queue changes to all devices other than the excluded list, use
!<device>
, for example,!eno1
.
-
Example wildcard syntax is as follows:
-
vendorID
: The network device vendor ID represented as a 16-bit hexadecimal number with a0x
prefix. deviceID
: The network device ID (model) represented as a 16-bit hexadecimal number with a0x
prefix.NoteWhen a
deviceID
is specified, thevendorID
must also be defined. A device that matches all of the device identifiers specified in a device entryinterfaceName
,vendorID
, or a pair ofvendorID
plusdeviceID
qualifies as a network device. This network device then has its net queues count set to the reserved CPU count.When two or more devices are specified, the net queues count is set to any net device that matches one of them.
-
Set the queue count to the reserved CPU count for all devices by using this example performance profile:
apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: manual spec: cpu: isolated: 3-51,54-103 reserved: 0-2,52-54 net: userLevelNetworking: true nodeSelector: node-role.kubernetes.io/worker-cnf: ""
Set the queue count to the reserved CPU count for all devices matching any of the defined device identifiers by using this example performance profile:
apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: manual spec: cpu: isolated: 3-51,54-103 reserved: 0-2,52-54 net: userLevelNetworking: true devices: - interfaceName: “eth0” - interfaceName: “eth1” - vendorID: “0x1af4” - deviceID: “0x1000” nodeSelector: node-role.kubernetes.io/worker-cnf: ""
Set the queue count to the reserved CPU count for all devices starting with the interface name
eth
by using this example performance profile:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: manual spec: cpu: isolated: 3-51,54-103 reserved: 0-2,52-54 net: userLevelNetworking: true devices: - interfaceName: “eth*” nodeSelector: node-role.kubernetes.io/worker-cnf: ""
Set the queue count to the reserved CPU count for all devices with an interface named anything other than
eno1
by using this example performance profile:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: manual spec: cpu: isolated: 3-51,54-103 reserved: 0-2,52-54 net: userLevelNetworking: true devices: - interfaceName: “!eno1” nodeSelector: node-role.kubernetes.io/worker-cnf: ""
Set the queue count to the reserved CPU count for all devices that have an interface name
eth0
,vendorID
of0x1af4
, anddeviceID
of0x1000
by using this example performance profile:apiVersion: performance.openshift.io/v2 kind: PerformanceProfile metadata: name: manual spec: cpu: isolated: 3-51,54-103 reserved: 0-2,52-54 net: userLevelNetworking: true devices: - interfaceName: “eth0” - vendorID: “0x1af4” - deviceID: “0x1000” nodeSelector: node-role.kubernetes.io/worker-cnf: ""
Apply the updated performance profile:
$ oc apply -f <your_profile_name>.yaml
Additional resources
14.6.2. Verifying the queue status
In this section, a number of examples illustrate different performance profiles and how to verify the changes are applied.
Example 1
In this example, the net queue count is set to the reserved CPU count (2) for all supported devices.
The relevant section from the performance profile is:
apiVersion: performance.openshift.io/v2 metadata: name: performance spec: kind: PerformanceProfile spec: cpu: reserved: 0-1 #total = 2 isolated: 2-8 net: userLevelNetworking: true # ...
Display the status of the queues associated with a device using the following command:
NoteRun this command on the node where the performance profile was applied.
$ ethtool -l <device>
Verify the queue status before the profile is applied:
$ ethtool -l ens4
Example output
Channel parameters for ens4: Pre-set maximums: RX: 0 TX: 0 Other: 0 Combined: 4 Current hardware settings: RX: 0 TX: 0 Other: 0 Combined: 4
Verify the queue status after the profile is applied:
$ ethtool -l ens4
Example output
Channel parameters for ens4: Pre-set maximums: RX: 0 TX: 0 Other: 0 Combined: 4 Current hardware settings: RX: 0 TX: 0 Other: 0 Combined: 2 1
- 1
- The combined channel shows that the total count of reserved CPUs for all supported devices is 2. This matches what is configured in the performance profile.
Example 2
In this example, the net queue count is set to the reserved CPU count (2) for all supported network devices with a specific vendorID
.
The relevant section from the performance profile is:
apiVersion: performance.openshift.io/v2 metadata: name: performance spec: kind: PerformanceProfile spec: cpu: reserved: 0-1 #total = 2 isolated: 2-8 net: userLevelNetworking: true devices: - vendorID = 0x1af4 # ...
Display the status of the queues associated with a device using the following command:
NoteRun this command on the node where the performance profile was applied.
$ ethtool -l <device>
Verify the queue status after the profile is applied:
$ ethtool -l ens4
Example output
Channel parameters for ens4: Pre-set maximums: RX: 0 TX: 0 Other: 0 Combined: 4 Current hardware settings: RX: 0 TX: 0 Other: 0 Combined: 2 1
- 1
- The total count of reserved CPUs for all supported devices with
vendorID=0x1af4
is 2. For example, if there is another network deviceens2
withvendorID=0x1af4
it will also have total net queues of 2. This matches what is configured in the performance profile.
Example 3
In this example, the net queue count is set to the reserved CPU count (2) for all supported network devices that match any of the defined device identifiers.
The command udevadm info
provides a detailed report on a device. In this example the devices are:
# udevadm info -p /sys/class/net/ens4 ... E: ID_MODEL_ID=0x1000 E: ID_VENDOR_ID=0x1af4 E: INTERFACE=ens4 ...
# udevadm info -p /sys/class/net/eth0 ... E: ID_MODEL_ID=0x1002 E: ID_VENDOR_ID=0x1001 E: INTERFACE=eth0 ...
Set the net queues to 2 for a device with
interfaceName
equal toeth0
and any devices that have avendorID=0x1af4
with the following performance profile:apiVersion: performance.openshift.io/v2 metadata: name: performance spec: kind: PerformanceProfile spec: cpu: reserved: 0-1 #total = 2 isolated: 2-8 net: userLevelNetworking: true devices: - interfaceName = eth0 - vendorID = 0x1af4 ...
Verify the queue status after the profile is applied:
$ ethtool -l ens4
Example output
Channel parameters for ens4: Pre-set maximums: RX: 0 TX: 0 Other: 0 Combined: 4 Current hardware settings: RX: 0 TX: 0 Other: 0 Combined: 2 1
- 1
- The total count of reserved CPUs for all supported devices with
vendorID=0x1af4
is set to 2. For example, if there is another network deviceens2
withvendorID=0x1af4
, it will also have the total net queues set to 2. Similarly, a device withinterfaceName
equal toeth0
will have total net queues set to 2.
14.6.3. Logging associated with adjusting NIC queues
Log messages detailing the assigned devices are recorded in the respective Tuned daemon logs. The following messages might be recorded to the /var/log/tuned/tuned.log
file:
An
INFO
message is recorded detailing the successfully assigned devices:INFO tuned.plugins.base: instance net_test (net): assigning devices ens1, ens2, ens3
A
WARNING
message is recorded if none of the devices can be assigned:WARNING tuned.plugins.base: instance net_test: no matching devices available
14.7. Debugging low latency CNF tuning status
The PerformanceProfile
custom resource (CR) contains status fields for reporting tuning status and debugging latency degradation issues. These fields report on conditions that describe the state of the operator’s reconciliation functionality.
A typical issue can arise when the status of machine config pools that are attached to the performance profile are in a degraded state, causing the PerformanceProfile
status to degrade. In this case, the machine config pool issues a failure message.
The Performance Addon Operator contains the performanceProfile.spec.status.Conditions
status field:
Status: Conditions: Last Heartbeat Time: 2020-06-02T10:01:24Z Last Transition Time: 2020-06-02T10:01:24Z Status: True Type: Available Last Heartbeat Time: 2020-06-02T10:01:24Z Last Transition Time: 2020-06-02T10:01:24Z Status: True Type: Upgradeable Last Heartbeat Time: 2020-06-02T10:01:24Z Last Transition Time: 2020-06-02T10:01:24Z Status: False Type: Progressing Last Heartbeat Time: 2020-06-02T10:01:24Z Last Transition Time: 2020-06-02T10:01:24Z Status: False Type: Degraded
The Status
field contains Conditions
that specify Type
values that indicate the status of the performance profile:
Available
- All machine configs and Tuned profiles have been created successfully and are available for cluster components are responsible to process them (NTO, MCO, Kubelet).
Upgradeable
- Indicates whether the resources maintained by the Operator are in a state that is safe to upgrade.
Progressing
- Indicates that the deployment process from the performance profile has started.
Degraded
Indicates an error if:
- Validation of the performance profile has failed.
- Creation of all relevant components did not complete successfully.
Each of these types contain the following fields:
Status
-
The state for the specific type (
true
orfalse
). Timestamp
- The transaction timestamp.
Reason string
- The machine readable reason.
Message string
- The human readable reason describing the state and error details, if any.
14.7.1. Machine config pools
A performance profile and its created products are applied to a node according to an associated machine config pool (MCP). The MCP holds valuable information about the progress of applying the machine configurations created by performance addons that encompass kernel args, kube config, huge pages allocation, and deployment of rt-kernel. The performance addons controller monitors changes in the MCP and updates the performance profile status accordingly.
The only conditions returned by the MCP to the performance profile status is when the MCP is Degraded
, which leads to performaceProfile.status.condition.Degraded = true
.
Example
The following example is for a performance profile with an associated machine config pool (worker-cnf
) that was created for it:
The associated machine config pool is in a degraded state:
# oc get mcp
Example output
NAME CONFIG UPDATED UPDATING DEGRADED MACHINECOUNT READYMACHINECOUNT UPDATEDMACHINECOUNT DEGRADEDMACHINECOUNT AGE master rendered-master-2ee57a93fa6c9181b546ca46e1571d2d True False False 3 3 3 0 2d21h worker rendered-worker-d6b2bdc07d9f5a59a6b68950acf25e5f True False False 2 2 2 0 2d21h worker-cnf rendered-worker-cnf-6c838641b8a08fff08dbd8b02fb63f7c False True True 2 1 1 1 2d20h
The
describe
section of the MCP shows the reason:# oc describe mcp worker-cnf
Example output
Message: Node node-worker-cnf is reporting: "prepping update: machineconfig.machineconfiguration.openshift.io \"rendered-worker-cnf-40b9996919c08e335f3ff230ce1d170\" not found" Reason: 1 nodes are reporting degraded status on sync
The degraded state should also appear under the performance profile
status
field marked asdegraded = true
:# oc describe performanceprofiles performance
Example output
Message: Machine config pool worker-cnf Degraded Reason: 1 nodes are reporting degraded status on sync. Machine config pool worker-cnf Degraded Message: Node yquinn-q8s5v-w-b-z5lqn.c.openshift-gce-devel.internal is reporting: "prepping update: machineconfig.machineconfiguration.openshift.io \"rendered-worker-cnf-40b9996919c08e335f3ff230ce1d170\" not found". Reason: MCPDegraded Status: True Type: Degraded
14.8. Collecting low latency tuning debugging data for Red Hat Support
When opening a support case, it is helpful to provide debugging information about your cluster to Red Hat Support.
The must-gather
tool enables you to collect diagnostic information about your OpenShift Container Platform cluster, including node tuning, NUMA topology, and other information needed to debug issues with low latency setup.
For prompt support, supply diagnostic information for both OpenShift Container Platform and low latency tuning.
14.8.1. About the must-gather tool
The oc adm must-gather
CLI command collects the information from your cluster that is most likely needed for debugging issues, such as:
- Resource definitions
- Audit logs
- Service logs
You can specify one or more images when you run the command by including the --image
argument. When you specify an image, the tool collects data related to that feature or product. When you run oc adm must-gather
, a new pod is created on the cluster. The data is collected on that pod and saved in a new directory that starts with must-gather.local
. This directory is created in your current working directory.
14.8.2. About collecting low latency tuning data
Use the oc adm must-gather
CLI command to collect information about your cluster, including features and objects associated with low latency tuning, including:
- The Performance Addon Operator namespaces and child objects.
-
MachineConfigPool
and associatedMachineConfig
objects. - The Node Tuning Operator and associated Tuned objects.
- Linux Kernel command line options.
- CPU and NUMA topology
- Basic PCI device information and NUMA locality.
To collect Performance Addon Operator debugging information with must-gather
, you must specify the Performance Addon Operator must-gather
image:
--image=registry.redhat.io/openshift4/performance-addon-operator-must-gather-rhel8:v4.10.
14.8.3. Gathering data about specific features
You can gather debugging information about specific features by using the oc adm must-gather
CLI command with the --image
or --image-stream
argument. The must-gather
tool supports multiple images, so you can gather data about more than one feature by running a single command.
To collect the default must-gather
data in addition to specific feature data, add the --image-stream=openshift/must-gather
argument.
Prerequisites
-
Access to the cluster as a user with the
cluster-admin
role. - The OpenShift Container Platform CLI (oc) installed.
Procedure
-
Navigate to the directory where you want to store the
must-gather
data. Run the
oc adm must-gather
command with one or more--image
or--image-stream
arguments. For example, the following command gathers both the default cluster data and information specific to the Performance Addon Operator:$ oc adm must-gather \ --image-stream=openshift/must-gather \ 1 --image=registry.redhat.io/openshift4/performance-addon-operator-must-gather-rhel8:v4.10 2
Create a compressed file from the
must-gather
directory that was created in your working directory. For example, on a computer that uses a Linux operating system, run the following command:$ tar cvaf must-gather.tar.gz must-gather.local.5421342344627712289/ 1
- 1
- Replace
must-gather-local.5421342344627712289/
with the actual directory name.
- Attach the compressed file to your support case on the Red Hat Customer Portal.
Additional resources
- For more information about MachineConfig and KubeletConfig, see Managing nodes.
- For more information about the Node Tuning Operator, see Using the Node Tuning Operator.
- For more information about the PerformanceProfile, see Configuring huge pages.
- For more information about consuming huge pages from your containers, see How huge pages are consumed by apps.