Welcome!

Containers Expo Blog Authors: Elizabeth White, Liz McMillan, Yeshim Deniz, Pat Romanski, Amit Gupta

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
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
SYS-CON Events announced today that Dasher Technologies will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Dasher Technologies, Inc. ® is a premier IT solution provider that delivers expert technical resources along with trusted account executives to architect and deliver complete IT solutions and services to help our clients execute their goals, plans and objectives. Since 1999, we'v...
SYS-CON Events announced today that TidalScale, a leading provider of systems and services, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale has been involved in shaping the computing landscape. They've designed, developed and deployed some of the most important and successful systems and services in the history of the computing industry - internet, Ethernet, operating s...
SYS-CON Events announced today that Massive Networks, that helps your business operate seamlessly with fast, reliable, and secure internet and network solutions, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. As a premier telecommunications provider, Massive Networks is headquartered out of Louisville, Colorado. With years of experience under their belt, their team of...
SYS-CON Events announced today that IBM has been named “Diamond Sponsor” of SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California.
Infoblox delivers Actionable Network Intelligence to enterprise, government, and service provider customers around the world. They are the industry leader in DNS, DHCP, and IP address management, the category known as DDI. We empower thousands of organizations to control and secure their networks from the core-enabling them to increase efficiency and visibility, improve customer service, and meet compliance requirements.
SYS-CON Events announced today that TidalScale will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale is the leading provider of Software-Defined Servers that bring flexibility to modern data centers by right-sizing servers on the fly to fit any data set or workload. TidalScale’s award-winning inverse hypervisor technology combines multiple commodity servers (including their ass...
As hybrid cloud becomes the de-facto standard mode of operation for most enterprises, new challenges arise on how to efficiently and economically share data across environments. In his session at 21st Cloud Expo, Dr. Allon Cohen, VP of Product at Elastifile, will explore new techniques and best practices that help enterprise IT benefit from the advantages of hybrid cloud environments by enabling data availability for both legacy enterprise and cloud-native mission critical applications. By rev...
Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant tha...
As popularity of the smart home is growing and continues to go mainstream, technological factors play a greater role. The IoT protocol houses the interoperability battery consumption, security, and configuration of a smart home device, and it can be difficult for companies to choose the right kind for their product. For both DIY and professionally installed smart homes, developers need to consider each of these elements for their product to be successful in the market and current smart homes.
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, will lead you through the exciting evolution of the cloud. He'll look at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering ...
SYS-CON Events announced today that N3N will exhibit at SYS-CON's @ThingsExpo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. N3N’s solutions increase the effectiveness of operations and control centers, increase the value of IoT investments, and facilitate real-time operational decision making. N3N enables operations teams with a four dimensional digital “big board” that consolidates real-time live video feeds alongside IoT sensor data a...
In a recent survey, Sumo Logic surveyed 1,500 customers who employ cloud services such as Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform (GCP). According to the survey, a quarter of the respondents have already deployed Docker containers and nearly as many (23 percent) are employing the AWS Lambda serverless computing framework. It’s clear: serverless is here to stay. The adoption does come with some needed changes, within both application development and operations. Tha...
SYS-CON Events announced today that Avere Systems, a leading provider of enterprise storage for the hybrid cloud, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Avere delivers a more modern architectural approach to storage that doesn't require the overprovisioning of storage capacity to achieve performance, overspending on expensive storage media for inactive data or the overbui...
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
SYS-CON Events announced today that mruby Forum will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. mruby is the lightweight implementation of the Ruby language. We introduce mruby and the mruby IoT framework that enhances development productivity. For more information, visit http://forum.mruby.org/.
Digital transformation is changing the face of business. The IDC predicts that enterprises will commit to a massive new scale of digital transformation, to stake out leadership positions in the "digital transformation economy." Accordingly, attendees at the upcoming Cloud Expo | @ThingsExpo at the Santa Clara Convention Center in Santa Clara, CA, Oct 31-Nov 2, will find fresh new content in a new track called Enterprise Cloud & Digital Transformation.
Amazon is pursuing new markets and disrupting industries at an incredible pace. Almost every industry seems to be in its crosshairs. Companies and industries that once thought they were safe are now worried about being “Amazoned.”. The new watch word should be “Be afraid. Be very afraid.” In his session 21st Cloud Expo, Chris Kocher, a co-founder of Grey Heron, will address questions such as: What new areas is Amazon disrupting? How are they doing this? Where are they likely to go? What are th...
Most technology leaders, contemporary and from the hardware era, are reshaping their businesses to do software. They hope to capture value from emerging technologies such as IoT, SDN, and AI. Ultimately, irrespective of the vertical, it is about deriving value from independent software applications participating in an ecosystem as one comprehensive solution. In his session at @ThingsExpo, Kausik Sridhar, founder and CTO of Pulzze Systems, will discuss how given the magnitude of today's applicati...