In this lab, you will use PerfView to determine why a .NET application is causing lots of garbage collections and allocating a large amount of memory. The application is called Jack Compiler, and it is a sample compiler for a fictional programming language called Jack. Specifically, this version of Jack Compiler is in fact a transpiler -- it converts Jack code to equivalent C code that can be compiled with any C compiler.
Open a command prompt and navigate to the bin folder. Run the following command:
JackCompiler.exe BigProgram.jack
Make note of the size of BigProgram.jack – it is under 500KB, but it still takes the JackCompiler.exe a very long time to compile it. Do not terminate the program. You will now use PerfView to determine why the compiler is misbehaving.
Run PerfView.exe and choose Collect > Collect from the menu. Make sure to check the .NET SampAlloc checkbox. When you’re done, click Start Collection.
After a few seconds, click Stop Collection and open the report in PerfView’s left pane. Double-click the CPU Stacks report, choose the JackCompiler process, and notice which methods are responsible for the highest CPU utilization.
Next, go back to the report file in PerfView’s left pane and double-click the GC Heap Net Mem (Coarse Sampling) Stacks report. Choose the JackCompiler process again. In the By Name tab, notice that the application is allocating mostly strings. Double-click the String row and expand the call tree until you determine which call path is responsible for most allocations.
Fix the application code (in the src folder) to avoid excessive allocations in this code path, and then measure it again. You should see a gigantic performance improvement.
Hint: Replace the
CompilationOutputTextWriterwith a simpleStringWriter.