|By Andreas Grabner||
|October 29, 2009 04:35 PM EDT||
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:
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.
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.
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:
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.
For IoT to grow as quickly as analyst firms’ project, a lot is going to fall on developers to quickly bring applications to market. But the lack of a standard development platform threatens to slow growth and make application development more time consuming and costly, much like we’ve seen in the mobile space. In his session at @ThingsExpo, Mike Weiner, Product Manager of the Omega DevCloud with KORE Telematics Inc., discussed the evolving requirements for developers as IoT matures and conducted a live demonstration of how quickly application development can happen when the need to comply wit...
Jul. 29, 2015 07:30 AM EDT Reads: 229
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Architect for the Internet of Things and Intelligent Systems, described how to revolutionize your archit...
Jul. 28, 2015 06:30 PM EDT Reads: 1,372
It is one thing to build single industrial IoT applications, but what will it take to build the Smart Cities and truly society-changing applications of the future? The technology won’t be the problem, it will be the number of parties that need to work together and be aligned in their motivation to succeed. In his session at @ThingsExpo, Jason Mondanaro, Director, Product Management at Metanga, discussed how you can plan to cooperate, partner, and form lasting all-star teams to change the world and it starts with business models and monetization strategies.
Jul. 28, 2015 04:30 PM EDT Reads: 1,752
The Internet of Everything (IoE) brings together people, process, data and things to make networked connections more relevant and valuable than ever before – transforming information into knowledge and knowledge into wisdom. IoE creates new capabilities, richer experiences, and unprecedented opportunities to improve business and government operations, decision making and mission support capabilities.
Jul. 28, 2015 04:00 PM EDT Reads: 219
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists addressed this very serious issue of profound change in the industry.
Jul. 28, 2015 03:00 PM EDT Reads: 1,247
Discussions about cloud computing are evolving into discussions about enterprise IT in general. As enterprises increasingly migrate toward their own unique clouds, new issues such as the use of containers and microservices emerge to keep things interesting. In this Power Panel at 16th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the state of cloud computing today, and what enterprise IT professionals need to know about how the latest topics and trends affect their organization.
Jul. 28, 2015 02:00 PM EDT Reads: 1,157
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Jul. 28, 2015 11:45 AM EDT Reads: 410
Converging digital disruptions is creating a major sea change - Cisco calls this the Internet of Everything (IoE). IoE is the network connection of People, Process, Data and Things, fueled by Cloud, Mobile, Social, Analytics and Security, and it represents a $19Trillion value-at-stake over the next 10 years. In her keynote at @ThingsExpo, Manjula Talreja, VP of Cisco Consulting Services, discussed IoE and the enormous opportunities it provides to public and private firms alike. She will share what businesses must do to thrive in the IoE economy, citing examples from several industry sectors.
Jul. 28, 2015 11:00 AM EDT Reads: 2,029
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Opening Keynote at 16th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, d...
Jul. 27, 2015 09:00 PM EDT Reads: 2,038
There will be 150 billion connected devices by 2020. New digital businesses have already disrupted value chains across every industry. APIs are at the center of the digital business. You need to understand what assets you have that can be exposed digitally, what their digital value chain is, and how to create an effective business model around that value chain to compete in this economy. No enterprise can be complacent and not engage in the digital economy. Learn how to be the disruptor and not the disruptee.
Jul. 27, 2015 10:00 AM EDT Reads: 2,019
Akana has released Envision, an enhanced API analytics platform that helps enterprises mine critical insights across their digital eco-systems, understand their customers and partners and offer value-added personalized services. “In today’s digital economy, data-driven insights are proving to be a key differentiator for businesses. Understanding the data that is being tunneled through their APIs and how it can be used to optimize their business and operations is of paramount importance,” said Alistair Farquharson, CTO of Akana.
Jul. 27, 2015 09:00 AM EDT Reads: 309
Business as usual for IT is evolving into a "Make or Buy" decision on a service-by-service conversation with input from the LOBs. How does your organization move forward with cloud? In his general session at 16th Cloud Expo, Paul Maravei, Regional Sales Manager, Hybrid Cloud and Managed Services at Cisco, discusses how Cisco and its partners offer a market-leading portfolio and ecosystem of cloud infrastructure and application services that allow you to uniquely and securely combine cloud business applications and services across multiple cloud delivery models.
Jul. 27, 2015 08:00 AM EDT Reads: 1,891
The enterprise market will drive IoT device adoption over the next five years. In his session at @ThingsExpo, John Greenough, an analyst at BI Intelligence, division of Business Insider, analyzed how companies will adopt IoT products and the associated cost of adopting those products. John Greenough is the lead analyst covering the Internet of Things for BI Intelligence- Business Insider’s paid research service. Numerous IoT companies have cited his analysis of the IoT. Prior to joining BI Intelligence, he worked analyzing bank technology for Corporate Insight and The Clearing House Payment...
Jul. 26, 2015 09:00 PM EDT Reads: 1,558
In his keynote at 16th Cloud Expo, Rodney Rogers, CEO of Virtustream, discussed the evolution of the company from inception to its recent acquisition by EMC – including personal insights, lessons learned (and some WTF moments) along the way. Learn how Virtustream’s unique approach of combining the economics and elasticity of the consumer cloud model with proper performance, application automation and security into a platform became a breakout success with enterprise customers and a natural fit for the EMC Federation.
Jul. 26, 2015 08:00 AM EDT Reads: 2,140
"Optimal Design is a technology integration and product development firm that specializes in connecting devices to the cloud," stated Joe Wascow, Co-Founder & CMO of Optimal Design, in this SYS-CON.tv interview at @ThingsExpo, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 25, 2015 02:00 PM EDT Reads: 379
SYS-CON Events announced today that CommVault has been named “Bronze Sponsor” of SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. A singular vision – a belief in a better way to address current and future data management needs – guides CommVault in the development of Singular Information Management® solutions for high-performance data protection, universal availability and simplified management of data on complex storage networks. CommVault's exclusive single-platform architecture gives companies unp...
Jul. 25, 2015 01:00 PM EDT Reads: 1,943
Electric Cloud and Arynga have announced a product integration partnership that will bring Continuous Delivery solutions to the automotive Internet-of-Things (IoT) market. The joint solution will help automotive manufacturers, OEMs and system integrators adopt DevOps automation and Continuous Delivery practices that reduce software build and release cycle times within the complex and specific parameters of embedded and IoT software systems.
Jul. 25, 2015 12:15 PM EDT Reads: 442
"ciqada is a combined platform of hardware modules and server products that lets people take their existing devices or new devices and lets them be accessible over the Internet for their users," noted Geoff Engelstein of ciqada, a division of Mars International, in this SYS-CON.tv interview at @ThingsExpo, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 25, 2015 12:00 PM EDT Reads: 1,521
Internet of Things is moving from being a hype to a reality. Experts estimate that internet connected cars will grow to 152 million, while over 100 million internet connected wireless light bulbs and lamps will be operational by 2020. These and many other intriguing statistics highlight the importance of Internet powered devices and how market penetration is going to multiply many times over in the next few years.
Jul. 25, 2015 09:00 AM EDT Reads: 1,480
SYS-CON Events announced today that Dyn, the worldwide leader in Internet Performance, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Dyn is a cloud-based Internet Performance company. Dyn helps companies monitor, control, and optimize online infrastructure for an exceptional end-user experience. Through a world-class network and unrivaled, objective intelligence into Internet conditions, Dyn ensures traffic gets delivered faster, safer, and more reliably than ever.
Jul. 24, 2015 11:00 PM EDT Reads: 2,044