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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 reserved

Using Memory Efficiently
Transparent page sharing
allows the VMkernel to use
physical memory efficiently.
The VMkernel detects identical
pages in virtual machines’
memory and maps them to the
same underlying physical page.



No changes to guest operating
system required

The VMkernel treats the shared
pages as copy-on-write.




Read-only when shared
Private copies after write

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

Supporting Higher Consolidation Ratios

Ample memory.
Balloon remains
uninflated.

Inflate balloon.
(Driver demands
memory from
guest operating
system.)
Deflate balloon.
(Driver relinquishes
memory.)

The VMware® Tools balloon driver
supports higher memory consolidation
ratios.



Deallocate memory from selected virtual
machines when RAM is scarce.

Guest is forced to page out to its own
paging area. The VMkernel reclaims
memory.

Guest can page in. Host
grants memory.

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

Using Resource Pools to Meet Business Needs
A resource pool:




Is a logical abstraction
for hierarchically
managing CPU and
memory resources
Is used on standalone
hosts or clusters
enabled for VMware
Distributed Resource
Scheduler (DRS)

A resource pool
provides resources for
virtual machines and
child pools.

resource
pools

root

resource
pool

Geography?
Department?
Function?
Hardware?

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

Resource Pool Settings
Resource pools have the following
attributes:






Shares



Low, Normal, High, Custom

Reservations, in MHz and MB
Limits, in MHz and MB



Unlimited access, by default (up to
maximum amount of resource
accessible)

Expandable reservation?





Yes – Virtual machines and
subpools can draw from this pool’s
parent.
No –...
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