esxiwindowscpu多核的设置原理详细说明-USB迷|专注于互联网分享

2024年4月16日发(作者：殳一禾)

These basic architectures are mixed in modern multiprocessor computers. Processors are grouped on a multicore CPU package or node.

Processors that belong to the same node share access to memory modules as with the UMA architecture. Also, processors can access

memory from the remote node via a shared interconnect. Processors do so for the NUMA architecture but with slower performance. This

memory access is performed through the CPU that owns that memory rather than directly.

NUMA nodes are CPU/Memory couples that consist of a CPU socket and the closest memory modules. NUMA is usually configured in

BIOS as the node interleaving or interleaved memory setting.

An example. An ESXi host has two sockets (two CPUs) and 256 GB of RAM. Each CPU has 6 processor cores. This server contains two

NUMA nodes. Each NUMA node has 1 CPU socket (one CPU), 6 Cores, and 128 GB of RAM.

always tries to allocate memory for a VM from a native (home) NUMA node. A home node can be changed automatically if there are

changes in VM loads and ESXi server loads.

Virtual NUMA (vNUMA) is the analog of NUMA for VMware virtual machines. A vNUMA consumes hardware resources of more than one

physical NUMA node to provide optimal performance. The vNUMA technology exposes the NUMA topology to a guest operating system.

As a result, the guest OS is aware of the underlying NUMA topology for the most efficient use. The virtual hardware version of a VM must

be 8 or higher to use vNUMA. Handling of vNUMA was significantly improved in VMware vSphere 6.5, and this feature is no longer

controlled by the CPU cores per socket value in the VM configuration. By default, vNUMA is enabled for VMs that have more than 8 logical

processors (vCPUs). You can enable vNUMA manually for a VM by editing the VMX configuration file of the VM and adding the

line =X, where X is the number of vCPUs for the virtual machine.

Calculations

Let’s find out how to calculate the number of physical CPU cores, logical CPU cores, and other parameters on a server.

The total number of physical CPU cores on a host machine is calculated with the formula:

(The number of Processor Sockets) x (The number of cores/processor) = The number of physical processor cores

*Processor sockets only with installed processors must be considered.

If hyper-threading is supported, calculate the number of logical processor cores by using the formula:

(The number of physical processor cores) x (2 threads/physical processor) = the number of logical processors

Finally, use a single formula to calculate available processor resources that can be assigned to VMs:

(CPU sockets) x (CPU cores) x (threads)

For example, if you have a server with two processors with each having 4 cores and supporting hyper-threading, then the total number of

logical processors that can be assigned to VMs is

2(CPUs) x 4(cores) x 2(HT) = 16 logical processors

One logical processor can be assigned as one processor or one CPU core for a VM in VM settings.

As for virtual machines, due to hardware emulation features, they can use multiple processors and CPU cores in their configuration for

operation. One physical CPU core can be configured as a virtual CPU or a virtual CPU core for a VM.

The total amount of clock cycles available for a VM is calculated as:

(The number of logical sockets) x (The clock speed of the CPU)

For example, if you configure a VM to use 2 vCPUs with 2 cores when you have a physical processor whose clock speed is 3.0 GHz, then

the total clock speed is 2x2x3=12 GHz. If CPU overcommitment is used on an ESXi host, the available frequency for a VM can be less than

calculated if VMs perform CPU-intensive tasks.

Limitations

The maximum number of virtual processor sockets assigned to a VM is 128. If you want to assign more than 128 virtual processors,

configure a VM to use multicore processors.

The maximum number of processor cores that can be assigned to a single VM is 768 in vSphere 7.0 Update 1. A virtual machine cannot

use more CPU cores than the number of logical processor cores on a physical machine.

CPU hot add. If a VM has 128 vCPUs or less than 128 vCPUs, then you cannot use the CPU hot add feature for this VM and edit the CPU

configuration of a VM while a VM is in the running state.

OS CPU restrictions. If an operating system has a limit on the number of processors, and you assign more virtual processors for a VM, the

additional processors are not identified and used by a guest OS. Limits can be caused by OS technical design and OS licensing

restrictions. Note that there are operating systems that are licensed per-socket and per CPU core (for example, ).

CPU support limits for some operating systems:

Windows 10 Pro – 2 CPUs

Windows 10 Home – 1 CPU

Windows 10 Workstation – 4 CPUs

Windows Server 2019 Standard/Datacenter – 64 CPUs

Windows XP Pro x64 – 2 CPUs

Windows 7 Pro/Ultimate/Enterprise - 2 CPUs

Windows Server 2003 Datacenter – 64 CPUs

Configuration Recommendations

For older vSphere versions, I recommend using sockets over cores in VM configuration. At first, you might not see a significant difference in

CPU sockets or CPU cores in VM configuration for VM performance. Be aware of some configuration features. Remember about NUMA

and vNUMA when you consider setting multiple virtual processors (sockets) for a VM to have optimal performance.

If vNUMA is not configured automatically, mirror the NUMA topology of a physical server. Here are some recommendations for VMs in

VMware vSphere 6.5 and later:

When you define the number of logical processors (vCPUs) for a VM, prefer the cores-per-socket configuration. Continue until the

count exceeds the number of CPU cores on a single NUMA node on the ESXi server. Use the same logic until you exceed the

amount of memory that is available on a single NUMA node of your physical ESXi server.

Sometimes, the number of logical processors for your VM configuration is more than the number of physical CPU cores on a single

NUMA node, or the amount of RAM is higher than the total amount of memory available for a single NUMA node. Consider dividing

the count of logical processors (vCPUs) across the minimum number of NUMA nodes for optimal performance.

Don’t set an odd number of vCPUs if the CPU count or amount of memory exceeds the number of CPU cores. The same applies in

case memory exceeds the amount of memory for a single NUMA node on a physical server.

Don’t create a VM that has a number of vCPUs larger than the count of physical processor cores on your physical host.

If you cannot disable vNUMA due to your requirements, don’t enable the vCPU Hot-Add feature.

If vNUMA is enabled in vSphere prior to version 6.5, and you have defined the number of logical processors (vCPUs) for a VM, select the

number of virtual sockets for a VM while keeping the cores-per-socket amount equal to 1 (that is the default value). This is because the one-

core-per-socket configuration enables vNUMA to select the best vNUMA topology to the guest OS automatically. This automatic

configuration is optimal on the underlying physical topology of the server. If vNUMA is enabled, and you’re using the same number of

logical processors (vCPUs) but increase the number of virtual CPU cores and reduce the number of virtual sockets by the same amount,

then vNUMA cannot set the best NUMA configuration for a VM. As a result, VM performance is affected and can degrade.

If a guest operating system and other software installed on a VM are licensed on a per-processor basis, configure a VM to use fewer

processors with more CPU cores. For example, Windows Server 2012 R2 is licensed per socket, and Windows Server 2016 is licensed on

a per-core basis.

If you use CPU overcommitment in the configuration of your VMware virtual machines, keep in mind these values:

1:1 to 3:1 – There should be no problems in running VMs

3:1 to 5:1 – Performance degradation is observed

6:1 – Prepare for problems caused by significant performance degradation

CPU overcommitment with normal values can be used in test and dev environments without risks.

Configuration of VMs on ESXi Hosts

First of all, determine how many logical processors (Total number of CPUs) of your physical host are needed for a virtual machine for

proper work with sufficient performance. Then define how many virtual sockets with processors (Number of Sockets in vSphere Client) and

how many CPU cores (Cores per Socket) you should set for a VM keeping in mind previous recommendations and limitations. The table

below can help you select the needed configuration.

If you need to assign more than 8 logical processors for a VM, the logic remains the same. To calculate the number of logical CPUs in ,

multiply the number of sockets by the number of cores. For example, if you need to configure a VM to use 2-processor sockets, each has 2

CPU cores, then the total number of logical CPUs is 2*2=4. It means that you should select 4 CPUs in the virtual hardware options of the

VM in vSphere Client to apply this configuration.

Let me explain how to configure CPU options for a VM in VMware vSphere Client. Enter the IP address of your in a web browser, and

open VMware vSphere Client. In the navigator, open Hosts and Clusters, and select the needed virtual machine that you want to configure.

Make sure that the VM is powered off to be able to change CPU configuration.

Right-click the VM, and in the context menu, hit Edit Settings to open virtual machine settings.

Expand the CPU section in the Virtual Hardware tab of the Edit Settings window.

CPU. Click the drop-down menu in the CPU string, and select the total number of needed logical processors for this VM. In this example, I

select 4 logical processors for the Ubuntu VM (blog-Ubuntu1).

Cores per Socket. In this string, click the drop-down menu, and select the needed number of cores for each virtual socket (processor).

CPU Hot Plug. If you want to use this feature, select the Enable CPU Hot Add checkbox. Remember limitations and requirements.

Reservation. Select the guaranteed minimum allocation of CPU clock speed (frequency, MHz, or GHz) for a virtual machine on an ESXi

host or cluster.

Limit. Select the maximum CPU clock speed for a VM processor. This frequency is the maximum frequency for a virtual machine, even if

this VM is the only VM running on the ESXi host or cluster with more free processor resources. The set limit is true for all virtual processors

of a VM. If a VM has 2 single-core processors, and the limit is 1000 MHz, then both virtual processors work with a total clock speed of one

million cycles per second (500 MHz for each core).

Shares. This parameter defines the priority of resource consumption by virtual machines (Low, Normal, High, Custom) on an ESXi host or

resource pool. Unlike Reservation and Limit parameters, the Shares parameter is applied for a VM only if there is a lack of CPU resources

within an ESXi host, resource pool, or DRS cluster.

Available options for the Shares parameter:

Low – 500 shares per a virtual processor

Normal - 1000 shares per a virtual processor

High - 2000 shares per a virtual processor

Custom – set a custom value

The higher the Shares value is, the higher the amount of CPU resources provisioned for a VM within an ESXi host or a resource pool.

Hardware virtualization. Select this checkbox to enable . This option is useful if you want to run a VM inside a VM for testing or educational

purposes.

Performance counters. This feature is used to allow an application installed within the virtual machine to be debugged and optimized after

measuring CPU performance.

Scheduling Affinity. This option is used to assign a VM to a specific processor. The entered value can be like this: “0, 2, 4-7”.

I/O MMU. This feature allows VMs to have direct access to hardware input/output devices such as storage controllers, network cards,

graphic cards (rather than using emulated or paravirtualized devices). I/O MMU is also called Intel Virtualization Technology for Directed

I/O (Intel VT-d) and AMD I/O Virtualization (AMD-V). I/O MMU is disabled by default. Using this option is deprecated in vSphere 7.0. If I/O

MMU is enabled for a VM, the VM cannot be migrated with and is not compatible with snapshots, memory overcommit, suspended VM

state, physical NIC sharing, and .

If you use a standalone ESXi host and use VMware Host Client to configure VMs in a web browser, the configuration principle is the same

as for VMware vSphere Client.

If you connect to vCenter Server or ESXi host in and open VM settings of a vSphere VM, you can edit the basic configuration of virtual

processors. Click VM > Settings, select the Hardware tab, and click Processors. On the following screenshot, you see processor

configuration for the same Ubuntu VM that was configured before in vSphere Client. In the graphical user interface (GUI) of VMware

Workstation, you should select the number of virtual processors (sockets) and the number of cores per processor. The number of total

processor cores (logical cores of physical processors on an ESXi host or cluster) is calculated and displayed below automatically. In the

interface of vSphere Client, you set the number of total processor cores (the CPUs option), select the number of cores per processor, and

then the number of virtual sockets is calculated and displayed.

Configuring VM Processors in PowerCLI

If you prefer using the command-line interface to configure components of VMware vSphere, use to edit the CPU configuration of VMs.

Let’s find out how to edit VM CPU configuration for a VM which name is Ubuntu 19 in Power CLI. The commands are used for VMs that are

powered off.

To configure a VM to use two single-core virtual processors (two virtual sockets are used), use the command:

get-VM -name Ubuntu19 | set-VM -NumCpu 2

Enter another number if you want to set another number of processors (sockets) to a VM.

In the following example, you see how to configure a VM to use two dual-core virtual processors (2 sockets are used):

$VM=Get-VM -Name Ubuntu19

$VMSpec=New-Object -Type lMachineConfigSpec -Property @{ "NumCoresPerSocket" = 2}

$igVM_Task($VMSpec)

$VM | Set-VM -NumCPU 2

Once a new CPU configuration is applied to the virtual machine, this configuration is saved in the VMX configuration file of the VM. In my

case, I check the file located in the VM directory on the datastore (/vmfs/volumes/datastore2/Ubuntu19/). Lines with new

CPU configuration are located at the end of the VMX file.

numvcpus = "2"

erSocket = "2"

If you need to reduce the number of processors (sockets) for a VM, use the same command as shown before with less quantity. For

example, to set one processor (socket) for a VM, use this command:

get-VM -name Ubuntu19 | set-VM -NumCpu 1

The main advantage of using Power CLI is the ability to configure multiple VMs in bulk. is important and convenient if the number of virtual

machines to configure is high. Use VMware cmdlets and syntax of Microsoft PowerShell to create scripts.

Conclusion

This blog post has covered the configuration of virtual processors for VMware vSphere VMs. Virtual processors for virtual machines are

configured in VMware vSphere Client and in Power CLI. The performance of applications running on a VM depends on the correct CPU

and memory configuration. In VMware vSphere 6.5 and later versions, set more cores in CPU for virtual machines and use the CPU cores

per socket approach. If you use vSphere versions older than vSphere 6.5, configure the number of sockets without increasing the number of

CPU cores for a VM due to different behavior of vNUMA in newer and older vSphere versions. Take into account the licensing model of

software you need to install on a VM. If the software is licensed on using a per CPU model, configure more cores per CPU in VM settings.

When using virtual machines in VMware vSphere, don’t forget about . Use NAKIVO Backup & Replication to back up your virtual machines,

including VMs that have multiple cores per CPU. Regular backup helps you protect your data and recover the data in case of a .

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