|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.
"At our booth we are showing how to provide trust in the Internet of Things. Trust is where everything starts to become secure and trustworthy. Now with the scaling of the Internet of Things it becomes an interesting question – I've heard numbers from 200 billion devices next year up to a trillion in the next 10 to 15 years," explained Johannes Lintzen, Vice President of Sales at Utimaco, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 17, 2014 07:30 PM EST Reads: 1,237
The Internet of Things is a misnomer. That implies that everything is on the Internet, and that simply should not be - especially for things that are blurring the line between medical devices that stimulate like a pacemaker and quantified self-sensors like a pedometer or pulse tracker. The mesh of things that we manage must be segmented into zones of trust for sensing data, transmitting data, receiving command and control administrative changes, and peer-to-peer mesh messaging. In his session at @ThingsExpo, Ryan Bagnulo, Solution Architect / Software Engineer at SOA Software, focused on desi...
Dec. 17, 2014 07:15 PM EST Reads: 1,153
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
Dec. 17, 2014 06:30 PM EST Reads: 1,084
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 17, 2014 06:00 PM EST Reads: 1,060
"For over 25 years we have been working with a lot of enterprise customers and we have seen how companies create applications. And now that we have moved to cloud computing, mobile, social and the Internet of Things, we see that the market needs a new way of creating applications," stated Jesse Shiah, CEO, President and Co-Founder of AgilePoint Inc., in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 17, 2014 06:00 PM EST Reads: 1,219
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
Dec. 17, 2014 11:45 AM EST Reads: 1,364
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Dec. 16, 2014 11:45 PM EST Reads: 1,189
Code Halos - aka "digital fingerprints" - are the key organizing principle to understand a) how dumb things become smart and b) how to monetize this dynamic. In his session at @ThingsExpo, Robert Brown, AVP, Center for the Future of Work at Cognizant Technology Solutions, outlined research, analysis and recommendations from his recently published book on this phenomena on the way leading edge organizations like GE and Disney are unlocking the Internet of Things opportunity and what steps your organization should be taking to position itself for the next platform of digital competition.
Dec. 15, 2014 11:45 PM EST Reads: 1,576
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
Dec. 15, 2014 10:30 AM EST Reads: 6,835
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at @ThingsExpo, Andrew Bolwell, Director of Innovation for HP's Printing and Personal Systems Group, discussed how key attributes of mobile technology – touch input, sensors, social, and ...
Dec. 15, 2014 10:00 AM EST Reads: 1,923
In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect at GE, and Ibrahim Gokcen, who leads GE's advanced IoT analytics, focused on the Internet of Things / Industrial Internet and how to make it operational for business end-users. Learn about the challenges posed by machine and sensor data and how to marry it with enterprise data. They also discussed the tips and tricks to provide the Industrial Internet as an end-user consumable service using Big Data Analytics and Industrial Cloud.
Dec. 15, 2014 10:00 AM EST Reads: 1,577
Building low-cost wearable devices can enhance the quality of our lives. In his session at Internet of @ThingsExpo, Sai Yamanoor, Embedded Software Engineer at Altschool, provided an example of putting together a small keychain within a $50 budget that educates the user about the air quality in their surroundings. He also provided examples such as building a wearable device that provides transit or recreational information. He then reviewed the resources available to build wearable devices at home including open source hardware, the raw materials required and the options available to power s...
Dec. 15, 2014 09:00 AM EST Reads: 1,579
Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, addressed the big issues involving these technologies and, more important, the results they will achieve. Rodney Rogers, chairman and CEO of Virtustream; Brendan O'Brien, co-founder of Aria Systems, Bart Copeland, president and CEO of ActiveState Software; Jim Cowie, chief scientist at Dyn; Dave Wagstaff, VP and chief architect at BSQUARE Corporation; Seth Proctor, CTO of NuoDB, Inc.; and Andris Gailitis, C...
Dec. 15, 2014 09:00 AM EST Reads: 1,405
There's Big Data, then there's really Big Data from the Internet of Things. IoT is evolving to include many data possibilities like new types of event, log and network data. The volumes are enormous, generating tens of billions of logs per day, which raise data challenges. Early IoT deployments are relying heavily on both the cloud and managed service providers to navigate these challenges. In her session at Big Data Expo®, Hannah Smalltree, Director at Treasure Data, discussed how IoT, Big Data and deployments are processing massive data volumes from wearables, utilities and other machines...
Dec. 15, 2014 08:45 AM EST Reads: 1,994
"There is a natural synchronization between the business models, the IoT is there to support ,” explained Brendan O'Brien, Co-founder and Chief Architect of Aria Systems, in this SYS-CON.tv interview at the 15th International Cloud Expo®, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 15, 2014 08:15 AM EST Reads: 2,679
SYS-CON Media announced that Splunk, a provider of the leading software platform for real-time Operational Intelligence, has launched an ad campaign on Big Data Journal. Splunk software and cloud services enable organizations to search, monitor, analyze and visualize machine-generated big data coming from websites, applications, servers, networks, sensors and mobile devices. The ads focus on delivering ROI - how improved uptime delivered $6M in annual ROI, improving customer operations by mining large volumes of unstructured data, and how data tracking delivers uptime when it matters most.
Dec. 15, 2014 06:45 AM EST Reads: 2,132
In this Women in Technology Power Panel at 15th Cloud Expo, moderated by Anne Plese, Senior Consultant, Cloud Product Marketing at Verizon Enterprise, Esmeralda Swartz, CMO at MetraTech; Evelyn de Souza, Data Privacy and Compliance Strategy Leader at Cisco Systems; Seema Jethani, Director of Product Management at Basho Technologies; Victoria Livschitz, CEO of Qubell Inc.; Anne Hungate, Senior Director of Software Quality at DIRECTV, discussed what path they took to find their spot within the technology industry and how do they see opportunities for other women in their area of expertise.
Dec. 15, 2014 04:00 AM EST Reads: 1,370
While great strides have been made relative to the video aspects of remote collaboration, audio technology has basically stagnated. Typically all audio is mixed to a single monaural stream and emanates from a single point, such as a speakerphone or a speaker associated with a video monitor. This leads to confusion and lack of understanding among participants especially regarding who is actually speaking. Spatial teleconferencing introduces the concept of acoustic spatial separation between conference participants in three dimensional space. This has been shown to significantly improve comprehe...
Dec. 12, 2014 05:00 PM EST Reads: 1,238
The Industrial Internet revolution is now underway, enabled by connected machines and billions of devices that communicate and collaborate. The massive amounts of Big Data requiring real-time analysis is flooding legacy IT systems and giving way to cloud environments that can handle the unpredictable workloads. Yet many barriers remain until we can fully realize the opportunities and benefits from the convergence of machines and devices with Big Data and the cloud, including interoperability, data security and privacy.
Dec. 11, 2014 06:00 PM EST Reads: 1,440
Performance is the intersection of power, agility, control, and choice. If you value performance, and more specifically consistent performance, you need to look beyond simple virtualized compute. Many factors need to be considered to create a truly performant environment. In his General Session at 15th Cloud Expo, Harold Hannon, Sr. Software Architect at SoftLayer, discussed how to take advantage of a multitude of compute options and platform features to make cloud the cornerstone of your online presence.
Dec. 11, 2014 03:15 PM EST Reads: 1,910