Welcome!

Containers Expo Blog Authors: Flint Brenton, Thanh Tran, Liz McMillan, Sujoy Sen, Scott Allen

Related Topics: Containers Expo Blog

Containers Expo Blog: Blog Post

The Problem with SLA Monitoring in Virtualized Environments

The time-keeping problem and how it impacts application performance

Because virtual machines work by time-sharing host physical hardware, a virtual machine cannot exactly duplicate the timing behaviour of a physical machine. This leads to the timekeeping problems explained in the VMWare White Paper about Timekeeping in Virtual Machines that results in inaccurate time measurements within the virtual machine. This affects ALL performance metrics that rely on the operating system clock time to keep track of time which includes system counters like CPU or I/O Utilization. Performance Management solutions therefore run into the problem that the monitored metrics are inaccurate and can lead to incorrect enforcement of SLAs or wrong assumptions about application performance.

This blog explains the time keeping problem, how it impacts Application Performance Management in virtualized environments and what can be done to solve this problem.

Time keeping problem explained

Operating Systems that use a Tick Counting approach to keep track of time use hardware interrupts to count how many ticks have occurred since the system started. In a virtualized environment these interrupts are consumed by the virtualization infrastructure which keeps track of what we call the “Real Time”. The interrupts are then forwarded to the hosted virtual machines which itself keep track of the time that we call “Apparent Time“. In the best case scenario Real Time and Apparent Time are the same:

Timekeeping - Phase 1 - Real and Apparent Time are the same

Timekeeping - Phase 1 - Real and Apparent Time are the same

A virtual machine is not “always on” as it gets descheduled by the virtual server because of time-sharing with other virtual machines. In that time the hardware interrupts cannot be handled by the virtual machine and are therefore put into a queue for later consumption.

Timekeeping - Phase 2 - Virtual Machine is descheduled

Timekeeping - Phase 2 - Virtual Machine is descheduled

At the time the Virtual Machine gets scheduled again the operating system’s Apparent Time is still the time it was before it got descheduled as it has not yet received the timer interrupts that happened in the meantime. In that case the Apparent Time has drifted from the Real Time. Impact: Any performance metric taken at this time only shows the time that the Virtual Machine believes had passed which is not the time that really passed.

Over time the Virtual Machine catches up with the interrupts it missed while descheduled.

 

Timekeeping - Phase 3 - Catching up with Time
Timekeeping – Phase 3 – Catching up with Time

There are several other techniques that virtualization environments use to bring the Apparent Time back to Real Time as fast as possible. For more details have a look at the VMWare White Paper as mentioned on the top of this blog.

Impacts of the Time Keeping Problem

Any time based metrics captured from within the Virtual Machine are subject to the timekeeping problem including CPU Utilization, Memory Allocations per time interval, I/O access per time interval,… and any custom time tracking that can be used for e.g.: response time or transaction time monitoring. Operating system counters like % CPU per process also runs into another interesting problem where individual processes might get charged incorrectly with time that they never consumed. After a Virtual Machine is resumed the queued timer interrupts are processed. These interrupts come in a faster rate than normal. The currently active processes are charged with all these timing events although they have not done any work in that time because they were actually descheduled.

You can see that the timekeeping issue can really mess up your performance counters. The more load you have on a virtual server, the more virtual machines there are to schedule and de-schedule – the higher the impact on accurate timing will be. Other side effects like over-provisioning of CPU or Memory have an impact as well.

Using performance metrics from within the Virtual Machine for application performance management and enforcement of Service Level Agreements is therefore very questionable as the results are not accurate and not predictable.

Accurate Time Keeping with Pseudo Performance Counters

VMWare is aware of this problem and explains in great detail the reasons and the effects in their White Paper. As a solution for performance management solutions VMWare provides a way to query the actual Real Time at any time from within the Virtual Machine. Pseudo Performance Counters are made available via virtual processor registers that can be accessed from any application within the Virtual Machine.

dynaTrace is using these new counters for accurate time measurement when Managing Application Performance in virtualized VMWare environments. This allows accurate SLA enforcement and application performance management down to individual transactions or even methods. The following illustration shows a single captured transaction with accurate timings. dynaTrace captures the Real and the Apparent Time on method and transaction level:

 

Accurate Timing on Transaction and Method Level
Accurate Timing on Transaction and Method Level

Capturing the Real Time values and also showing the Apparent Time Drift enables Application Performance Management with accurate timing values. Accurate timings are the basics for accurate SLA Enforcement in Production as well as Application Performance Monitoring.

Is timekeeping a real issue in your environment?

The timekeeping problem is well known within the VMWare community and brings challenges to accurate application performance management in virtualized environments. I am interested in your experience with this problem. Have you been aware of it? Do you live with the inaccuracy or do you have other approaches for accurate measuring? Please share your thoughts on this topic.

More Stories By Andreas Grabner

Andreas Grabner has been helping companies improve their application performance for 15+ years. He is a regular contributor within Web Performance and DevOps communities and a prolific speaker at user groups and conferences around the world. Reach him at @grabnerandi

@ThingsExpo Stories
In his session at 18th Cloud Expo, Bruce Swann, Senior Product Marketing Manager at Adobe, will discuss how the Adobe Marketing Cloud can help marketers embrace opportunities for personalized, relevant and real-time customer engagement across offline (direct mail, point of sale, call center) and digital (email, website, SMS, mobile apps, social networks, connected objects). Bruce Swann has more than 15 years of experience working with digital marketing disciplines like web analytics, social med...
SYS-CON Events announced today that ContentMX, the marketing technology and services company with a singular mission to increase engagement and drive more conversations for enterprise, channel and SMB technology marketers, has been named “Sponsor & Exhibitor Lounge Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York City, New York. “CloudExpo is a great opportunity to start a conversation with new prospects, but what happens after the...
WebRTC is bringing significant change to the communications landscape that will bridge the worlds of web and telephony, making the Internet the new standard for communications. Cloud9 took the road less traveled and used WebRTC to create a downloadable enterprise-grade communications platform that is changing the communication dynamic in the financial sector. In his session at @ThingsExpo, Leo Papadopoulos, CTO of Cloud9, will discuss the importance of WebRTC and how it enables companies to fo...
SYS-CON Events announced today Object Management Group® has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
The IoT is changing the way enterprises conduct business. In his session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, discuss how businesses can gain an edge over competitors by empowering consumers to take control through IoT. We'll cite examples such as a Washington, D.C.-based sports club that leveraged IoT and the cloud to develop a comprehensive booking system. He'll also highlight how IoT can revitalize and restore outdated business models, making them profitable...
The IoTs will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, will demonstrate how to move beyond today's coding paradigm and share the must-have mindsets for removing complexity from the development proc...
Customer experience has become a competitive differentiator for companies, and it’s imperative that brands seamlessly connect the customer journey across all platforms. With the continued explosion of IoT, join us for a look at how to build a winning digital foundation in the connected era – today and in the future. In his session at @ThingsExpo, Chris Nguyen, Group Product Marketing Manager at Adobe, will discuss how to successfully leverage mobile, rapidly deploy content, capture real-time d...
What a difference a year makes. Organizations aren’t just talking about IoT possibilities, it is now baked into their core business strategy. With IoT, billions of devices generating data from different companies on different networks around the globe need to interact. From efficiency to better customer insights to completely new business models, IoT will turn traditional business models upside down. In the new customer-centric age, the key to success is delivering critical services and apps wit...
Join us at Cloud Expo | @ThingsExpo 2016 – June 7-9 at the Javits Center in New York City and November 1-3 at the Santa Clara Convention Center in Santa Clara, CA – and deliver your unique message in a way that is striking and unforgettable by taking advantage of SYS-CON's unmatched high-impact, result-driven event / media packages.
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, will provide an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life ...
SYS-CON Events announced today that BMC Software has been named "Siver Sponsor" of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. BMC is a global leader in innovative software solutions that help businesses transform into digital enterprises for the ultimate competitive advantage. BMC Digital Enterprise Management is a set of innovative IT solutions designed to make digital business fast, seamless, and optimized from mainframe to mo...
SYS-CON Events announced today that MobiDev will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex software systems for startups and enterprises. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobile software company with over 200 develope...
SoftLayer operates a global cloud infrastructure platform built for Internet scale. With a global footprint of data centers and network points of presence, SoftLayer provides infrastructure as a service to leading-edge customers ranging from Web startups to global enterprises. SoftLayer's modular architecture, full-featured API, and sophisticated automation provide unparalleled performance and control. Its flexible unified platform seamlessly spans physical and virtual devices linked via a world...
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
Companies can harness IoT and predictive analytics to sustain business continuity; predict and manage site performance during emergencies; minimize expensive reactive maintenance; and forecast equipment and maintenance budgets and expenditures. Providing cost-effective, uninterrupted service is challenging, particularly for organizations with geographically dispersed operations.
As cloud and storage projections continue to rise, the number of organizations moving to the cloud is escalating and it is clear cloud storage is here to stay. However, is it secure? Data is the lifeblood for government entities, countries, cloud service providers and enterprises alike and losing or exposing that data can have disastrous results. There are new concepts for data storage on the horizon that will deliver secure solutions for storing and moving sensitive data around the world. ...
SYS-CON Events announced today TechTarget has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. TechTarget is the Web’s leading destination for serious technology buyers researching and making enterprise technology decisions. Its extensive global networ...
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
SYS-CON Events announced today that MangoApps will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. MangoApps provides modern company intranets and team collaboration software, allowing workers to stay connected and productive from anywhere in the world and from any device. For more information, please visit https://www.mangoapps.com/.
The essence of data analysis involves setting up data pipelines that consist of several operations that are chained together – starting from data collection, data quality checks, data integration, data analysis and data visualization (including the setting up of interaction paths in that visualization). In our opinion, the challenges stem from the technology diversity at each stage of the data pipeline as well as the lack of process around the analysis.