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Expert Q&A: Virtualization EditionApril 26th, 2013

Welcome

Adam Kalsey

Voxeo Labs, Tropo Product

Mgr

Chris Spearman

PSSC Labs, Big Data Systems

Architect

Darren Schreiber

Founder, 2600hz

Our Panelists

Could it all be so simple?

In VoIP, It’s all about Timing

Because virtual machines work by time-sharing host

physical hardware, they cannot exactly duplicate the

timing activity of physical machines. VMware® virtual

machines use several techniques to minimize and

conceal differences in timing performance, but the

differences can still sometimes cause timekeeping

inaccuracies and other problems in software running

in a virtual machine.

Source: http://www.vmware.com/files/pdf/techpaper/Timekeeping-In-VirtualMachines.pdf

Because virtual machines work by time-sharing host

physical hardware, they cannot exactly

duplicate the timing activity of physical

machines. VMware® virtual machines use several

techniques to minimize and conceal differences in

timing performance, but the differences can still

sometimes cause timekeeping inaccuracies and other

problems in software running in a virtual machine.

Because virtual machines work by time-sharing host

physical hardware, they cannot exactly

duplicate the timing activity of physical

machines. VMware® virtual machines use several

techniques to minimize and conceal differences in

timing performance, but the differences can still

sometimes cause timekeeping inaccuracies

and other problems in software running in a virtual

machine.

Some background…

KVM is to VMWare As FreeSWITCH is to Asterisk

• KVM (Kernal Virtual Machine) is the open-source

equivalent of VMWare.

• Released in 2007 as part of Linux 2.6.20

• KVM is playing “catch-up” to VMWare

• Almost full feature parity

• KVM doesn’t hold your hand as much

• VMWare is more abstracted

• Less customization to get VMWare boxes up

• Better abstraction in VMWare

• KVM is leaner than VMWare

• KVM > VMWare for timing• VMWare > KVM for ease of use• VMWare is the most abstracted virtualization software

• Easy to use• Lots of overhead (messes with timing)

• KVM is less abstracted• Devices are not plug and play• Can’t easily share devices/ports on the same box in

different VMs• Lean, mean and fast!

Platform Differences

A few quick notes on Hardware Assisted Virtualization

• First Introduced by IBM in 1972 for use in the VM/370

• VMWare first got x86 chips for virtualization in 2006• Hardware assisted virtualization is closer to native• Lots of performance benefits (theoretically)

• Early Hardware virtualization was actually slower

• KVM got later access to virtualization hardware

Timing: Whose Fault is it?• Is it the Host operating system?

• Or the Virtualization?

VMWare says it’s the host:

Many host operating systems do not provide a way for

the virtual machine to request a physical timer interrupt at

a precisely specified time.

Lost ticks

•Timing is kept in ticks

• Ticks have a known rate and are used for measuring time

•Virtual Machines cannot call the tick command, and try to “catch up”

when they miss ticks

•This phenomenon is called “lost ticks”

•The solution?

• In current VMware products, if the backlog of interrupts grows beyond

60 seconds, the virtual machine gives up on catching up, simply setting

its record of the backlog to zero.

What causes this?

In current VMware products, if the backlog of

interrupts grows beyond 60 seconds, the

virtual machine gives up on catching up,

simply setting its record of the

backlog to zero.

When can you Virtualize?Sometimes.

Why Virtualize?

Manage lots of Blocks.

• Virtualization introduces overhead

• Overhead effects timing

• Timing effects latency sensitive

applications

Example???

Recap

Microsoft Campus

w/ Overhead

NOPE

• Because of overhead

• Microsoft Introduced Latency

• Which delayed Carbon Neutrality but

saved $140,000.

Moral: Know the impact of your

overhead, in application and

operations

Latency

QUESTIONS???