CPU/MMU configuration

[greegthegeek]

Author : Kristina Bliznashka

URL : http:////docs.vmware.com/en/VMware-vSphere/6.0/com.vmware.vsphere.hostclient.doc/GUID-36E772F7-3512-49BA-8FA9-60D6DA961560.html

Topic Name : Change CPU/MMU Virtualization Settings in the vSphere Client

Publication Name : vSphere Administration with the vSphere Client

Product/Version : VMware vSphere/6.0

Question :

Hi there, Would you please be more specific on relation between CPU/MMU configuration and the Hardware virtualization: Expose Hardware assisted Virtualization to the guest OS button activation? Thanks!

[NathanosBlightc]

As respect to the physical hardware architecture of Processor/Memory (CPU/MMU) management, also for a VM we should configure how to assign physical resources of the host and grant access to hardware by the VMs. In this section you must set processor and page file access requests by the VM management method. Do you need to set it to choose and handle automatically by server platform or set exactly by the CPU virtualization technologies (AMD-V / Intel VT-x) and MMU (page file allocation) technologies (AMD RVI / Intel EPT)

For more details please see following links:

https://www.vmware.com/pdf/Perf_ESX_Intel-EPT-eval.pdf

Difference between AMD-v/Intel VT-x and AMD-Vi/Intel VT-d

[greegthegeek]

Hello Amin,

Yes, I understood the purpose of the policy, but what is the effect to choose one of the third policy without checking "Hardware virtualization: Expose Hardware assisted Virtualization to the guest OS" boxes?

[NathanosBlightc]

Ass VMware Mention:

software MMU has a higher overhead memory requirement than hardware MMU. So, to support software MMU, maximum overhead supported for virtual machine limit in the VMkernel needs to be increased...

Also to take advantage of all features that virtual hardware version 13 provides, use the default hardware MMU setting.

However all of the CPU-related virtualization features are mainly used for processing enhancement and ability to create and manage virtual resources from physical computing assets includes memory access and moving data across I/O devices. CPU/MMU how to work is about to provide by hardware technologies or software level.

[greegthegeek]

Ho!

I think I got it :smileyhappy:

Correct me if i'm wrong:

1. Hardware virtualization: Expose Hardware assisted Virtualization for the guest OS
2. CPU/MMU Virtualization: Expose Hardware assisted Virtualization for the HOST.

Am I finally right?

[NathanosBlightc]

Let me explain more accurately: If there is no hardware-assisted MMU then VM guest OS will keep guest virtual memory to guest physical memory address mappings into guest page tables, while ESXi maintains “shadow page tables” that directly map guest virtual memory to host physical memory addresses.    

[greegthegeek]

Hi Amin,

Thnaks for your time.

In understood MMU hardware assisted will avoid the use of guest shadow tables, and roughly, the result is to reduce latency to access to page tables.

But what about the CPU? Why can we activate CPU hardware virtualization here ("CPU/MMU virtualization: Hardware CPU, software MMU") and also on the other parameters ("Hardware virtualization: Expose hardware assisted virutalization to the guest os")?

What are the differences between the two CPU features? Because when i red documentation for "CPU/MMU virtualization: Hardware CPU, software MMU" and "Hardware virtualization: Expose hardware assisted virutalization to the guest os" they are talking together about using VT-X.

So my understanding is the following:

- Do your VM are 64 bits are need to make nested virtualization? Check Expose hardware assisted virutalization to the guest os

     => Guest optimization

- Do you have VT-X/AMD-V instructions? To optimize VMWare VMM mechanisms, select CPU Hardware.

     => Host optimization

- Do you have Intel EPT/AMD NPT instructions? To optimize VMWare VMM mechanisms, select MMU Hardware.

     => Host optimization

AM I correct & do you agree?

Thanks A LOT for your time :smileywink:

Greg

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[NathanosBlightc]

Yes I'm agree with you, absolutely it's a great conclusion. thanks for yourself buddy :smileywink: