Vmware

Allocating Compute Resources to Business
Functions

© 2011 VMware Inc. All rights reserved

CPU Management Supports Server Consolidation
A virtual machine can have up to 32 virtual CPUs (vCPUs).

When a vCPU must be scheduled, the
VMkernel maps a vCPU to a hardware execution context (HEC).
A hardware execution context is a processor’s capability to schedule one thread of execution.




HEC

HEC

HEC

A core or a hyperthread
VMkernel load balances

All the vCPUs in a virtual machine are scheduled at the same time.
HEC

HEC

HEC

HEC

VMware v Sphere: Overview – Revision A
© 2011 VMware Inc. All rights reserved

How Virtual Machines Compete for Resources
Proportional-share system for relative resource management:





Applied during resource contention
Prevents virtual machines from monopolizing resources

Guarantees predictable resource shares
Number of shares

Change number of shares Power on VM
Power off VM
VMware v Sphere: Overview – Revision A
© 2011 VMware Inc. All rights reserved

Limits, Reservations, and Shares,

Limit



This value is the cap on the consumption of CPU time by this virtual machine, measured in MHz.

Reservation




This value is the number of CPU cycles reserved for this virtual machine, measured in MHz.
The VMkernel chooses which CPUs it can migrate.

Shares



Having more shares means that this virtual machine will win competitions for CPU time more often.

VMware v Sphere: Overview – Revision A
© 2011 VMware Inc. All rights reserved

Virtual Memory Management

Virtual memory



This is memory mapped by an application inside the guest operating system.

application

Physical memory



Host presents virtual machines with physical pages.

guest OS

Machine memory



This represents actual pages allocated by host from RAM.

hypervisor

VMware v Sphere: Overview – Revision A
© 2011 VMware Inc. All rights