Optimizing Performance and Responsiveness

Customers expect high-performing and responsive systems. This encompasses a broad scope of scenarios ranging from boot time to fluid user interactions with applications. Analyzing performance problems requires a lot of expertise and domain-specific knowledge. Microsoft provides tools to help you tackle this complex task.

This guide introduces you to the process of measuring, analyzing, and solving the root causes of performance issues in key areas. Topics include:

• Using the Windows Performance Toolkit (WPT)

• Capturing event trace log (ETL) traces

• Boot, application launch, and UI delays

• CPU and disk resource usage analysis

• Critical path and wait analysis

Goals

This guide will show you how to perform the following tasks:

• Gather relevant data to analyze performance problems on any system

• Understand the analysis process to look at system resource consumption like CPU and disk

• Identify what can impact the system responsiveness in some key Windows scenarios

Tools

The Windows Assessment Toolkit in the ADK provides a set of performance-related tests called assessments. The assessment results are used to diagnose potential problems, so that the hardware and software that you develop are both responsive and have a minimal impact on battery life, startup performance, and shutdown time. The same assessments are available to OEM/ISV/IHV partners, enthusiasts, and other members of the community, to establish a common framework to measure, compare, and review aspects of quality.

The Windows Performance Toolkit consists of two independent tools: Windows Performance Recorder (WPR) and Windows Performance Analyzer (WPA). WPR is a powerful recording tool that creates Event Tracing for Windows (ETW) recordings. You can run WPR from the user interface (UI) or from the command line (CL). WPR provides built-in profiles that you can use to select the events you want to record. WPA is a powerful analysis tool that combines a flexible UI with extensive graphing capabilities and data tables that can be pivoted and have full text search capabilities.

Fast Startup Behavior

Introduced in Windows 8, Fast Startup is the default boot behavior. The shutdown process was updated to include writing data to disk in a way that mirrors how hibernate works. During boot, the system goes through the phases that are described in the following table.

For more information about Fast Startup Behavior, see the On/Off Transition Performance topic on MSDN.

CPU Scheduling and Threads

Because the number of processors in a system is limited, all threads cannot be run at the same time. Windows implements processor time-sharing, which allows a thread to run for a period of time before the processor switches to another thread. The act of switching between threads is called a context-switch and is performed by a Windows component called the dispatcher. Each thread exists in a particular execution state at any given time. Windows uses three states that are relevant to performance: Running, Ready, and Waiting.

Threads being executed are in the Running state. Threads that can execute, but are currently not running, are in the Ready state. Threads that cannot run (because they are waiting for a particular event) are in the Waiting state. The following figure illustrates the possible thread transitions.

1. A thread in the Running state initiates a transition to the Waiting state by calling a wait function such as WaitForSingleObject or Sleep(> 0).

2. A running thread or kernel operation readies a thread in the Waiting state (for example, SetEvent or timer expiration).

3. A thread in the Ready state is scheduled for processing by the dispatcher when a running thread waits or reaches the end of its quantum of execution.

4. A thread in the Running state is switched out and placed into the Ready state by the dispatcher when it is preempted by a higher priority thread or when its quantum ends.

Thread state becomes an important factor in performance only when a user is waiting for a thread to complete an operation.

For more information about CPU Scheduling, see the CPU Analysis topic on MSDN.

Exercises

This guide consists of the following exercises.

• Exercise 1 - Evaluate Fast Startup Using the Assessment Toolkit

• Exercise 2 - Evaluate Fast Startup Using Windows Performance Toolkit

• Exercise 3 - Understand Critical Path and Wait Analysis