31.01.2021

Category: Kvm numa

Kvm numa

Computers can have more than one system bus which allows them to have multiple processors in a single system like the one shown below:. This allows the servers to achieve higher compute capability at a better price to performance ratio, or to just exceed the possible compute power limitations of a single socket machine.

Each CPU has it's own block of memory that it can access at low latency. However sometimes the CPU will need to access memory attached to another socket. This is called remote memory access and the high latency this requires can leave processors under utilized. Such systems can be great as KVM hosts as it allows you to host more guests on a single machine. Since remote memory access causes high latency, you probably want to ensure that a guest is isolated to one CPU socket and its local memory, whilst spreading the guests out across the multiple areas.

Thus on a quad socket system, you could have 4 guests that never effect each other in any way and each run on their own CPUs and memory spaces. For details on how you can use cputune and numatune declarations to optimize the performance of your guests, read this. Now I will go on to explain how to use the numa declaration inside the cpu block to set up a NUMA topology inside the guest e.

This can be necessary if a guest is granted access to multiple CPU Sockets, or if you want to enable hotplugging of memory.

kvm numa

This tells the guest that it has 2 memory busses, each with 3 GiB of memory, and that cores have low latency access to one of the 3GB sets, whilst have low latency access to the other set.

Applications that can be optimized for NUMA will be able to take this into account so that they try to limit the number of remote memory calls they make. You probably want this to reflect your host's topology for optimal performance. I probably woudn't even bother giving a guest access to more than one node.

Most consumer and entry-level server hardware will only have 1 NUMA cell, so you probably don't want to have more than one cell declaration. You can find out how many NUMA cells you have by running lscpu. For example, for my KVM host I get the following:. If you want to fetch statistics about your NUMA nodes, such as how often they are making remote memory calls, then look into numastat.

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Setting KVM processor affinities. This section covers setting processor and processing core affinities with libvirt and KVM guests. By default, libvirt provisions guests using the hypervisor's default policy. For most hypervisors, the policy is to run guests on any available processing core or CPU. A guest on a NUMA system should be pinned to a processing core so that its memory allocations are always local to the node it is running on. This avoids cross-node memory transports which have less bandwidth and can significantly degrade performance.

The virsh nodeinfo command provides information about how many sockets, cores and hyperthreads there are attached a host. The output shows that that the system has a NUMA architecture. NUMA is more complex and requires more data to accurately interpret. Use the virsh capabilities to get additional output data on the CPU configuration.

This system has two sockets, therefore we can infer that each socket is a separate NUMA node. For a guest with four virtual CPUs, it would be optimal to lock the guest to physical CPUs 0 to 3, or 4 to 7 to avoid accessing non-local memory, which are significantly slower than accessing local memory.

Isolate CPU Resources in a NUMA Node on KVM

Running across multiple NUMA nodes significantly degrades performance for physical and virtualized tasks. Use the virsh freecell command to display the free memory on all NUMA nodes. Node 0 only has 2. Extract from the virsh capabilities output. The guest can be locked to a set of CPUs by appending the cpuset attribute to the configuration file.

While the guest is offline, open the configuration file with virsh edit. Locate where the guest's virtual CPU count is specified. Find the vcpus element.

Automatically locking guests to CPUs with virt-install The virt-install provisioning tool provides a simple way to automatically apply a 'best fit' NUMA policy when guests are created. The cpuset option for virt-install can use a CPU set of processors or the parameter auto.

Tuning CPU affinity on running guests There may be times where modifying CPU affinities on running guests is preferable to rebooting the guest. The virsh vcpuinfo and virsh vcpupin commands can perform CPU affinity changes on running guests. The virsh vcpuinfo command gives up to date information about where each virtual CPU is running.

The virsh vcpuinfo command confirms the change in affinity.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

CPU Pinning and NUMA Awareness in OpenStack

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I ran the command lscpu and got the following output:. Learn more. Asked 2 years, 5 months ago. Active 2 years, 4 months ago. Viewed times.

kvm numa

Damian Damian 13 13 bronze badges. Does your machine actually have multiple NUMA nodes or are you trying to fake it? Didn't know you could use a forward slash as a continuation character in batch files. Squashman I should've specified that I added that for clarity, it doesn't actually work like that. You can then continue to put each line of your code on a separate line as long as you end it with a caret.

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The Overflow Blog.It relies on setting up a virtual machine as the test environment and requires support for nested virtualization since plain QEMU is not sufficiently functional. The entire test process will take place inside a large virtual machine running Fedora The tests will require support for nested KVM, which is not enabled by default on hypervisor hosts.

When the virt-viewer application displays the installer, follow the defaults for the installation with a couple of exceptions:. The automatic disk partition setup can be optionally tweaked to reduce the swap space allocated.

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Once the installation process has completed, the virtual machine will reboot into the final operating system. It is now ready to deploy an OpenStack development environment. At this point a fairly standard devstack setup can be done with one exception: we should enable the NUMATopologyFilter filter, which we will use later.

KVM - NUMA Declaration

For example:. Fix that now to avoid later surprises after reboots:. We can validate this by querying the nova database. For example with object versioning fields removed :.

9.3. libvirt NUMA Tuning

To do the changes, the VM instance that is running devstack must be shut down:. At the same time we want to define the NUMA topology of the guest. Before starting OpenStack services again, it is necessary to explicitly set the libvirt virtualization type to KVM, so that guests can take advantage of nested KVM:. The first thing is to check that the compute node picked up the new NUMA topology setup for the guest:.

The guest should be locked to a single host NUMA node too. Boot a guest with the m1. This should operate in an identical manner to the default behavior where no NUMA policy is set. To define the topology we will create a new flavor:.

As a further sanity test, check what nova recorded for the instance in the database. Now getting more advanced we tell nova that the guest will have two NUMA nodes. To define the topology we will change the previously defined flavor:.

kvm numa

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3. See all OpenStack Legal Documents. Toggle navigation. Testing NUMA related hardware setup with libvirt.Avoid unnecessarily splitting resources across NUMA nodes. Use the numastat tool to view per-NUMA-node memory statistics for processes and the operating system. In the following example, the numastat tool shows four virtual machines with suboptimal memory alignment across NUMA nodes: numastat -c qemu-kvm Per-node process memory usage in MBs PID Node 0 Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Total qemu-kvm 68 16 2 3 qemu-kvm 11 5 18 1 92 qemu-kvm 62 22 qemu-kvm 3 1 2 12 0 0 Total You can run numad to align the guests' CPUs and memory resources automatically.

However, it is highly recommended to configure guest resource alignment using libvirt instead:. To verify that the memory has veen aligned, run numastat -c qemu-kvm again. The following output shows successful resource alignment: numastat -c qemu-kvm Per-node process memory usage in MBs PID Node 0 Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Total qemu-kvm 0 0 7 0 0 1 0 qemu-kvm 0 0 7 0 0 0 0 qemu-kvm 0 0 7 0 0 0 1 qemu-kvm 0 0 0 0 0 0 0 Total 0 0 0 0 Running numastat with -c provides compact output; adding the -m option adds system-wide memory information on a per-node basis to the output.

Refer to the numastat man page for more information. For optimal performance results, memory pinning should be used in combination with pinning of vCPU threads as well as other hypervisor threads.

Since vCPUs run as user-space tasks on the host operating system, pinning increases cache efficiency.

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One example of this is an environment where all vCPU threads are running on the same physical socket, therefore sharing a L3 cache domain. The lstopo tool can be used to visualize NUMA topology.

kvm numa

It can also help verify that vCPUs are binding to cores on the same physical socket. Pinning causes increased complexity when there are many more vCPUs than physical cores.

The vCPU thread is pinned to its own cpuset. There is a direct relationship between the vcpu and vcpupin tags.

How to KVM/QEMU tuning of NUMA and memory

If a vcpupin option is not specified, the value will be automatically determined and inherited from the parent vcpu tag option. Domain Processes. Here are the common uses of Markdown. Learn more Close.Forums New posts Search forums. What's new New posts Latest activity. Members Current visitors New profile posts Search profile posts. Log in. Search Everywhere Threads This forum This thread.

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Thread starter robertbovens Start date Jan 12, JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Jan 3, 9 0 1 Hello, i am trying to pin cpus to a numa node but find it difficult to understand why it is not working, i have the impression it is a bug, maybe someone can enlighten me with the issue i have. Feb 1, 4, 31 Vienna. CPU index 8 should be smaller than maxcpus 4. When i assign 4 cores to the vm, it will be automatically 0 1 2 3.

For me it doesnt make any sense why i would want or need to specify that again in the numa config. Will cpu pinning be supported in the future? Would be nice if it would be able to pin those through the gui Now i have a duel socket ibm m4bd server with only 16GB. I notice the vms go slower over time and when i use numastat i can see node misses. I also get a log irq took to long or something like that, not behind the computer at this moment.

You must log in or register to reply here. Share: Email Link. Top Bottom. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register. By continuing to use this site, you are consenting to our use of cookies. Accept Learn more….Avoid unnecessarily splitting resources across NUMA nodes.

Use the numastat tool to view per-NUMA-node memory statistics for processes and the operating system. In the following example, the numastat tool shows four virtual machines with suboptimal memory alignment across NUMA nodes: numastat -c qemu-kvm Per-node process memory usage in MBs PID Node 0 Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Total qemu-kvm 68 16 2 3 qemu-kvm 11 5 18 1 92 qemu-kvm 62 22 qemu-kvm 3 1 2 12 0 0 Total Run numad to align the guests' CPUs and memory resources automatically.

Then run numastat -c qemu-kvm again to view the results of running numad. The following output shows that resources have been aligned: numastat -c qemu-kvm Per-node process memory usage in MBs PID Node 0 Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Total qemu-kvm 0 0 7 0 0 1 0 qemu-kvm 0 0 7 0 0 0 0 qemu-kvm 0 0 7 0 0 0 1 qemu-kvm 0 0 0 0 0 0 0 Total 0 0 0 0 Running numastat with -c provides compact output; adding the -m option adds system-wide memory information on a per-node basis to the output.

See the numastat man page for more information. You can use the nodestats. This script also reports how much memory is strictly bound to certain host nodes for each running domain.

For example:. Nearly all memory is consumed on each domain MemFree. There are four domains virtual machines running: domain 'rhel' has 1. To print host NUMA node statistics, create a nodestats. The specific path to the script can be displayed by using the rpl -ql libvirt-python command. Since vCPUs run as user-space tasks on the host operating system, pinning increases cache efficiency. One example of this is an environment where all vCPU threads are running on the same physical socket, therefore sharing a L3 cache domain.

In Red Hat Enterprise Linux versions 7. However, with Red Hat Enterprise Linux 7. The lstopo tool can be used to visualize NUMA topology. It can also help verify that vCPUs are binding to cores on the same physical socket. Pinning causes increased complexity where there are many more vCPUs than physical cores. The vCPU thread is pinned to its own cpuset. There is a direct relationship between the vcpu and vcpupin tags.

If a vcpupin option is not specified, the value will be automatically determined and inherited from the parent vcpu tag option. Domain Processes. As provided in Red Hat Enterprise Linux, libvirt uses libnuma to set memory binding policies for domain processes.

The nodeset for these policies can be configured either as static specified in the domain XML or auto configured by querying numad.


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