Profiling Silverlight 4 with Visual Studio 2010

Silverlight is now into its fourth version (woo!) and with each iteration the platform becomes more solid, more mature and easier to develop for. One of the newer features that is now supported "out of the box" with Silverlight 4 is the ability to profile your Silverlight application, but you wouldn't know it from just digging around the menus of Visual Studio. In this post we'll explore the process of collecting a profile from your XAP (both in and out of browser) and we'll touch on common troubleshooting techniques for failed profiles.

What You'll Need

1. Visual Studio 2010 Ultimate or Premium (check out the product comparison, under "debugging", to see if your version has profiling support)

2. Silverlight 4 for Developers (includes the tools for Visual Studio)

   Note: you can't profile the normal version of the Silverlight plugin (there's a bit of registry and file magic that will be missing)

Ready, Set, Profile!

Here's the quick and easy way to profile - open an elevated Visual Studio 2010 Command Prompt (pre configured with useful Visual Studio commands) and run the following:

 VSPerfClrEnv /sampleon
VSPerfCmd -start:sample -output:somefile.vsp
VSPerfCmd -globalon
VSPerfCmd -launch:"c:\Program Files (x86)\Internet Explorer\iexplore.exe" -args:""
VSPerfCmd -shutdown
VSPerfClrEnv /off

This will create a VSP (Visual Studio Profile) file in the current directory, which you can then open in Visual Studio.

Note: If you plan on profiling Internet Explorer 8 (and up) you must disable its per-tab process feature (otherwise you'll end up profiling the iexplore container process instead of the process that is hosting Silverlight). You can find more information here.

Tips & Tricks / FAQ (Recommended Reading)

Take a couple of minutes and run through the following, since you are most likely going to run into one of these issues on your first go...

• Can I Profile Silverlight 3 Projects?

  You can only profile a Silverlight 3 project if it is running under the Silverlight 4 plugin. There are moves to release the supporting files to allow profiling of Silverlight 3, but now that Silverlight 4 is out the point is perhaps moot.

• Associate VSP Files with Visual Studio

  This one makes it easy to open VSP files directly from the command prompt (and aides in symbol resolution) - try to open a VSP from Explorer and when it asks you which program to use, select devenv.exe

• Symbols Fail to Resolve when opening VSP

  If the missing symbols are in Microsoft DLLs, make sure you have selected the public symbol server in your debugging options in Visual Studio under Tools->Options->Debugging->Symbols.

  If the missing symbols are in your own DLLs (like from your own XAP) then make sure to either launch the VSP from the directory that has your PDB files (see the above suggestion regarding associating VSP files with Visual Studio), or add the directories with your PDB files to your symbol path by adding them under the same tool window as above.

• Can I Start Profiling After Launching my Target?

  Sure - you just need to change the order a bit:

   VSPerfClrEnv /sampleon
  VSPerfCmd -start:sample -output:somefile.vsp
  VSPerfCmd -launch:"c:\Program Files (x86)\Internet Explorer\iexplore.exe" -args:""
  VSPerfCmd -globalon
  VSPerfCmd -shutdown
  VSPerfClrEnv /off
  

• Can I Stop Profiling Without Closing the Target?

  You bet!

   VSPerfClrEnv /sampleon
  VSPerfCmd -start:sample -output:somefile.vsp
  VSPerfCmd -globalon
  VSPerfCmd -launch:"c:\Program Files (x86)\Internet Explorer\iexplore.exe" -args:""
  VSPferfCmd -detach
  VSPerfClrEnv /off
  

• My profile doesn't have any of my functions!

  This is probably the most common problem and there are a couple of things to check:

  1. With the VSP open pull up the "Modules" view - if there are some GUIDs in the list of modules, then your code was picked up, but Visual Studio couldn't find your symbols - continue to the next step

  2. Pull up the Output window (usually Alt+2, View->Output) and you'll see a list of symbols that were loaded:

      Loaded symbols for C:\Windows\SYSTEM32\ntdll.dll.
     Loaded symbols for c:\Program Files\Microsoft Silverlight\4.0.50401.0\npctrl.dll.
     Loaded symbols for c:\Program Files\Microsoft Silverlight\4.0.50401.0\agcore.dll.
     Loaded symbols for C:\Windows\system32\WINMM.dll.
     ...
     

     You may also see one of the two following possible warnings:

      Failed to load symbols for C:\Windows\System32\nlaapi.dll.
     

     The most common problem - Visual Studio has found the DLL that it profiled, but it can't find the symbols for it. You'll need to adjust your symbol path to find the PDB files for your project and then reload the VSP.

      Warning VSP2701: Kit3D.dll could not be found when looking for symbol information.
     

     This is what you'll see if you're profiling a XAP from the internet - Visual Studio can't find the DLL that it profiled (because it was in the XAP that was downloaded) and thus can't load it to find corresponding PDBs. Load the VSP from the directory that has your DLLs in them (or add that to your global PATH), or download the XAP and extract the DLLs and this warning will go away. Note that if you don't have the PDBs then the warning will just morph into the above "Failed to load symbols".

  3. Your DLLs are not in the list: Make sure that you launch the command to profile from the Visual Studio Command Prompt. Failure to do so will result in a bunch of native DLLs being profiled, but no managed code.

  4. Your code isn't doing enough work: Although a little less likely for heavy apps, some simple apps simply don't do enough work. The profiler is sample based, meaning that it will take a snapshot (sample) of the call stack every so often. If the time spent in your code is extremely little, due to your code being so fast, it is likely that the profiler will simply miss your code. You can increase the amount of collected samples, to increase the likelihood of hitting your code by running something like:

      VSPerfCmd -timer:5000000
     

     This controls how often we sample by specifying the number of cycles before sampling (default is 10,000,000). You can also play around with -pf (sample of every n page faults) and -sys (sample on every n system calls). See -? for more info...

• Can I attach to a Running Process?

  Yes & No. You can attach to any process that was started within an environment that had the profiling variables set (so for example, any program you launch from a command prompt after running "VSPerfClrEnv /sampleon"). If you attach to a process that wasn't started within the correct environment you will only get native call stacks and no managed code. To attach to a PID use:

   VSPerfCmd -attach:PID
  

• Which Modules are Silverlight Itself?

  Silverlight is made up mainly of native code which can be found in two DLLs, agcore.dll and npctrl.dll. Can you guess why the ag?

• Why isn't Silverlight support baked into the IDE?

  Stay tuned (both for a stopgap and a final solution).

• When will we see debug symbols MS?

  This was a question on Maxim's blog - I'm not sure what the poster was actually getting at though. Microsoft publishes symbols for all released versions of Silverlight (and some select pre-release versions). These symbols are always the retail symbols - there are no CHK builds (or similar) for Silverlight with extended symbols. All of the information that you would want should be in the public symbols - I would love to hear about something that is missing...

• I Want More Options!

  This is an important one - check out:

   VSPerfCmd -?
  

  For a wide range of options, a lot of which I haven't touched on here.

26/4/2010 Edit: Maxim has a great post which walks you through profiling an actual app using similar steps to those described here - worth checking out!

28/4/2010 Edit: Updated FAQ with some questions from Maxim's blog

29/4/2010 Edit: Added note about IE8

Originally published here.