system Resource Management

The libvirt command manages VM system resources, such as vCPU and virtual memory resources.

Before you start:

Managing vCPU

CPU Shares

Overview

In a virtualization environment, multiple VMs on the same host compete for physical CPUs. To prevent some VMs from occupying too many physical CPU resources and affecting the performance of other VMs on the same host, you need to balance the vCPU scheduling of VMs to prevent excessive competition for physical CPUs.

The CPU share indicates the total capability of a VM to compete for physical CPU computing resources. You can set cpu_shares to specify the VM capacity to preempt physical CPU resources. The value of cpu_shares is a relative value without a unit. The CPU computing resources obtained by a VM are the available computing resources of physical CPUs (excluding reserved CPUs) allocated to VMs based on the CPU shares. Adjust the CPU shares to ensure the service quality of VM CPU computing resources.

Procedure

Change the value of cpu_shares allocated to the VM to balance the scheduling between vCPUs.

  • Check the current CPU share of the VM.

    # virsh schedinfo <VMInstance>
    Scheduler      : posix
    cpu_shares     : 1024
    vcpu_period    : 100000
    vcpu_quota     : -1
    emulator_period: 100000
    emulator_quota : -1
    global_period  : 100000
    global_quota   : -1
    iothread_period: 100000
    iothread_quota : -1
    
  • Online modification: Run the virsh schedinfo command with the –live parameter to modify the CPU share of a running VM.

    # virsh schedinfo <VMInstance> --live cpu_shares=<number>
    

    For example, to change the CPU share of the running openEulerVM from 1024 to 2048, run the following commands:

    # virsh schedinfo openEulerVM --live cpu_shares=2048
    Scheduler      : posix
    cpu_shares     : 2048
    vcpu_period    : 100000
    vcpu_quota     : -1
    emulator_period: 100000
    emulator_quota : -1
    global_period  : 100000
    global_quota   : -1
    iothread_period: 100000
    iothread_quota : -1
    

    The modification of the cpu_shares value takes effect immediately. The running time of the openEulerVM is twice the original running time. However, the modification will become invalid after the VM is shut down and restarted.

  • Permanent modification: Run the virsh schedinfo command with the –config parameter to change the CPU share of the VM in the libvirt internal configuration.

    # virsh schedinfo <VMInstance> --config cpu_shares=<number>
    

    For example, run the following command to change the CPU share of openEulerVM from 1024 to 2048:

    # virsh schedinfo openEulerVM --config cpu_shares=2048
    Scheduler      : posix
    cpu_shares     : 2048
    vcpu_period    : 0
    vcpu_quota     : 0
    emulator_period: 0
    emulator_quota : 0
    global_period  : 0
    global_quota   : 0
    iothread_period: 0
    iothread_quota : 0
    

    The modification on cpu_shares does not take effect immediately. Instead, the modification takes effect after the openEulerVM is started next time and takes effect permanently. The running time of the openEulerVM is twice that of the original VM.

Binding the QEMU Process to a Physical CPU

Overview

You can bind the QEMU main process to a specific physical CPU range, ensuring that VMs running different services do not interfere with adjacent VMs. For example, in a typical cloud computing scenario, multiple VMs run on one physical machine, and they carry diversified services, causing different degrees of resource occupation. To avoid interference of a VM with dense-storage I/O to an adjacent VM, storage processes that process I/O of different VMs need to be completely isolated. The QEMU main process handles frontend and backend services. Therefore, isolation needs to be implemented.

Procedure

Run the virsh emulatorpin command to bind the QEMU main process to a physical CPU.

  • Check the range of the physical CPU bound to the QEMU process:

    # virsh emulatorpin openEulerVM
    emulator: CPU Affinity
    ----------------------------------
           *: 0-63
    

    This indicates that the QEMU main process corresponding to VM openEulerVM can be scheduled on all physical CPUs of the host.

  • Online binding: Run the vcpu emulatorpin command with the –live parameter to modify the binding relationship between the QEMU process and the running VM.

    # virsh emulatorpin openEulerVM --live 2-3
    
    # virsh emulatorpin openEulerVM
    emulator: CPU Affinity
    ----------------------------------
           *: 2-3
    

    The preceding commands bind the QEMU process corresponding to VM openEulerVM to physical CPUs 2 and 3. That is, the QEMU process is scheduled only on the two physical CPUs. The binding relationship takes effect immediately but becomes invalid after the VM is shut down and restarted.

  • Permanent binding: Run the virsh emulatorpin command with the –config parameter to modify the binding relationship between the VM and the QEMU process in the libvirt internal configuration.

    # virsh emulatorpin openEulerVM --config 0-3,^1
    
    # virsh emulatorpin euler
    emulator: CPU Affinity
    ----------------------------------
           *: 0,2-3
    

    The preceding commands bind the QEMU process corresponding to VM openEulerVM to physical CPUs 0, 2 and 3. That is, the QEMU process is scheduled only on the three physical CPUs. The modification of the binding relationship does not take effect immediately. Instead, the modification takes effect after the next startup of the VM and takes effect permanently.

Adjusting the vCPU Binding Relationship

Overview

The vCPU of a VM is bound to a physical CPU. That is, the vCPU is scheduled only on the bound physical CPU to improve VM performance in specific scenarios. For example, in a NUMA system, vCPUs are bound to the same NUMA node to prevent cross-node memory access and VM performance deterioration. If the vCPU is not bound, by default, the vCPU can be scheduled on any physical CPU. The specific binding policy is determined by the user.

Procedure

Run the virsh vcpupin command to adjust the binding relationship between vCPUs and physical CPUs.

  • View the vCPU binding information of the VM.

     # virsh vcpupin openEulerVM
     VCPU   CPU Affinity
    ----------------------
     0      0-63
     1      0-63
     2      0-63
     3      0-63
    

    This indicates that all vCPUs of VM openEulerVM can be scheduled on all physical CPUs of the host.

  • Online adjustment: Run the vcpu vcpupin command with the –live parameter to modify the vCPU binding relationship of a running VM.

     # virsh vcpupin openEulerVM  --live 0 2-3
    
     # virsh vcpupin euler
     VCPU   CPU Affinity
    ----------------------
     0      2-3
     1      0-63
     2      0-63
     3      0-63
    

    The preceding commands bind vCPU 0 of VM openEulerVM to pCPU 2 and pCPU 3. That is, vCPU 0 is scheduled only on the two physical CPUs. The binding relationship takes effect immediately but becomes invalid after the VM is shut down and restarted.

  • Permanent adjustment: Run the virsh vcpupin command with the –config parameter to modify the vCPU binding relationship of the VM in the libvirt internal configuration.

     # virsh vcpupin openEulerVM --config 0 0-3,^1
    
     # virsh vcpupin openEulerVM
     VCPU   CPU Affinity
    ----------------------
     0      0,2-3
     1      0-63
     2      0-63
     3      0-63
    

    The preceding commands bind vCPU 0 of VM openEulerVM to physical CPUs 0, 2, and 3. That is, vCPU 0 is scheduled only on the three physical CPUs. The modification of the binding relationship does not take effect immediately. Instead, the modification takes effect after the next startup of the VM and takes effect permanently.

Managing Virtual Memory

Introduction to NUMA

Traditional multi-core computing uses the symmetric multi-processor (SMP) mode. Multiple processors are connected to a centralized memory and I/O bus. All processors can access only the same physical memory. Therefore, the SMP system is also referred to as a uniform memory access (UMA) system. Uniformity means that a processor can only maintain or share a unique value for each data record in memory at any time. Obviously, the disadvantage of SMP is its limited scalability, because when the memory and the I/O interface are saturated, adding a processor cannot obtain higher performance.

The non-uniform memory access architecture (NUMA) is a distributed memory access mode. In this mode, a processor can access different memory addresses at the same time, which greatly improves concurrency. With this feature, a processor is divided into multiple nodes, each of which is allocated a piece of local memory space. The processors of all nodes can access all physical memories, but the time required for accessing the memory on the local node is much shorter than that on a remote node.

Configuring Host NUMA

To improve VM performance, you can specify NUMA nodes for a VM using the VM XML configuration file before the VM is started so that the VM memory is allocated to the specified NUMA nodes. This feature is usually used together with the vCPU to prevent the vCPU from remotely accessing the memory.

Procedure

  • Check the NUMA topology of the host.

     # numactl -H
    available: 4 nodes (0-3)
    node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
    node 0 size: 31571 MB
    node 0 free: 17095 MB
    node 1 cpus: 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
    node 1 size: 32190 MB
    node 1 free: 28057 MB
    node 2 cpus: 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
    node 2 size: 32190 MB
    node 2 free: 10562 MB
    node 3 cpus: 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63
    node 3 size: 32188 MB
    node 3 free: 272 MB
    node distances:
    node   0   1   2   3
      0:  10  15  20  20
      1:  15  10  20  20
      2:  20  20  10  15
      3:  20  20  15  10
    
  • Add the numatune field to the VM XML configuration file to create and start the VM. For example, to allocate NUMA node 0 on the host to the VM, configure parameters as follows:

      <numatune>
        <memory mode="strict" nodeset="0"/>
      </numatune>
    

    If the vCPU of the VM is bound to the physical CPU of node 0, the performance deterioration caused by the vCPU accessing the remote memory can be avoided.

    NOTE:

    • The sum of memory allocated to the VM cannot exceed the remaining available memory of the NUMA node. Otherwise, the VM may fail to start.
    • You are advised to bind the VM memory and vCPU to the same NUMA node to avoid the performance deterioration caused by vCPU access to the remote memory. For example, bind the vCPU to NUMA node 0 as well.

Configuring Guest NUMA

Many service software running on VMs is optimized for the NUMA architecture, especially for large-scale VMs. openEuler provides the Guest NUMA feature to display the NUMA topology in VMs. You can identify the structure to optimize the performance of service software and ensure better service running.

When configuring guest NUMA, you can specify the location of vNode memory on the host to implement memory block binding and vCPU binding so that the vCPU and memory on the vNode are on the same physical NUMA node.

Procedure

After Guest NUMA is configured in the VM XML configuration file, you can view the NUMA topology on the VM. <numa> is mandatory for Guest NUMA.

  <cputune>
    <vcpupin vcpu='0' cpuset='0-3'/>
    <vcpupin vcpu='1' cpuset='0-3'/>
    <vcpupin vcpu='2' cpuset='16-19'/>
    <vcpupin vcpu='3' cpuset='16-19'/>
  </cputune>
  <numatune>
    <memnode cellid="0" mode="strict" nodeset="0"/>
    <memnode cellid="1" mode="strict" nodeset="1"/>
  </numatune>
  [...]
  <cpu>
    <numa>
      <cell id='0' cpus='0-1' memory='2097152'/>
      <cell id='1' cpus='2-3' memory='2097152'/>
    </numa>
  </cpu>

NOTE:

  • <numa> provides the NUMA topology function for VMs. cell id indicates the vNode ID, cpus indicates the vCPU ID, and memory indicates the memory size on the vNode.
  • If you want to use Guest NUMA to provide better performance, configure <numatune> and <cputune> so that the vCPU and memory are distributed on the same physical NUMA node.
  • cellid in <numatune> corresponds to cell id in <numa>. mode can be set to strict (apply for memory from a specified node strictly. If the memory is insufficient, the application fails.), preferred (apply for memory from a node first. If the memory is insufficient, apply for memory from another node), or interleave (apply for memory from a specified node in cross mode).; nodeset indicates the specified physical NUMA node.
  • In <cputune>, you need to bind the vCPU in the same cell id to the physical NUMA node that is the same as the memnode.
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