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Analyzing Performance Results
It is difficult to demonstrate the benefit of sampling profiling in a demonstration application that may only contain a couple of hundred lines of code, but for real-world applications that can contain dozens of DLLs and hundreds of thousands of lines of code, using sampling profiling to narrow down a performance problem is critical. Instrumentation sampling collects a huge amount of data, and it is easy to end up with a profile report spanning tens of gigabytes that is very slow to process both from a software and developer perspective.
(continued)Once a specific group of projects has been identified as the source of performance problems, instrumentation profiling makes tracking down the results relatively straightforward. The results of a profiling session, as shown in Figure 4, comprise information categorized in a number of different views accessible via a dropdown menu, as shown in Figure 5.
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Figure 5: Performance Results.
For blatant performance problems, the Performance Summary Screen often can identify the performance-problem culprit with the % of time in method figures. For more subtle performance problems, switching to the other pages in the performance report will be required. The Call Tree View presents the call tree of an application along with the number of time a method has been called. There are also many other columns that can be added, including the ability to inspect the actual time spent in methods (both inclusive and exclusive timings) and function line number (for sampling profiling only). The other two views that are helpful for finding performance problems are the Caller/Callee View and the Functions view.
Managed Code Profiling
In addition to the native code profiling capabilities covered so far, the VSTS Code Profiler is equally capable profiling C#, Visual Basic.NET, and C++/CLI managed code. The basics of managed code profiling are the same as native code profiling, but there are a number of different options that deal with managed code-specific problems. The most significant difference is the ability to collect information about the allocation and lifetime of managed objects. As the lifetime of managed objects is controlled by the .NET garbage collector, diagnosing problems related to excessive memory consumption can be more difficult in .NET projects. Turning on the collection of .NET memory statistic is accomplished by bringing up the Properties of a Performance Session from the Performance Explorer window, and selecting the options shown in Figure 6.
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Figure 6: Enabling Managed Memory Tracking.
The results of profiling a C++/CLI Windows forms application are shown in Figures 7 and 8. The results in Figure 7 will be available when the Collect .NET object allocation information checkbox is selected, and Figure 8 is available when is selected. As the figures show, the information is displayed by type, and while this can be useful for diagnosing general issues with over-allocation of a type, per-type allocation and lifetime information is a lot less useful than per-object statistics that tools like the SciTech MemProfiler.
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Figure 7: Selecting the Collect .NET object allocation information checkbox.
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Figure 8: Choosing Also collect .NET object lifetime information.
Conclusion
Improvements in the performance and features of the VSTS profiler that come with the VSTS 2008 release make the profiler a very capable performance-tuning tool for the C++ (and other VSTS language) developer. The use of two profiling modes makes the profiler capable of scaling to the largest of C++ code bases, and finding the most obscure performance problem can be accomplished using the wealth of information produced by instrumentation profiling. Developers who haven't settled on a preferred profiler will be well served by giving the VSTS Developer Edition Profiler a spin and seeing how well it fits their performance tuning needs.
About the Author
Nick Wienholt is an independent Windows and .NET consultant based in Sydney. He is the author of Maximizing .NET Performance and co-author of A Programmers Introduction to C# 2.0 from Apress, and specialises in system-level software architecture and development, with a particular focus of performance, security, interoperability, and debugging.
Nick is a keen and active participant in the .NET community. He is the co-founder of the Sydney Deep .NET User group and writes technical articles for Australian Developer Journal, ZDNet, Pinnacle Publishing, CodeGuru, MSDN Magazine (Australia and New Zealand Edition) and the Microsoft Developer Network. An archive of Nick's SDNUG presentations, articles, and .NET blog is available at www.dotnetperformance.com.
In recognition of his work in the .NET area, he was awarded the Microsoft Most Valued Professional Award from 2002 through 2007.
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