Why does a WPF app in a VM perform better than one running direct in the OS?

Question

We have a higher-end Win7-64 Dell precision workstation notebook with an i7, 8 gigs of ram, tons of hd space and running dedicated AMD graphics. The machine is about a month old. It was one of the highest-end we could get at the time.

What we're experiencing is when we run our WPF/SQL Server (local) app, it tends to hang and stall, sometimes completely crashing, but mostly just hanging until we force it to close. However, the exact same installer running in a VMware virtual machine running on that same machine runs flawlessly. Actually, the VM install runs better than a lot of native installs on other machines. It's very snappy with no hangs or hesitations at all. But again, same app, same installer running direct in the OS, and we're back to the issues above.

We've ran all Windows updates.... we've tried completely reinstalling everything... .NET frameworks, SQL Server, video drivers, even updated the BIOS and checked for rogue services but it still happens.

At first we thought it was Symantec AV's real-time protection because when we first shut that off, things started getting snappy again (and slowed down and froze when it auto-re-enabled itself furthering this hypothesis) but then it just started slowing down again, and more surprising, that same AV is running in the VM without issue! Checked the exceptions but there weren't any.

We even tried forcing WPF to run in software-render mode but again, nothing.

Now the odd thing is this only seems to be happening on this and a few other machines, but we can't seem to find anything in common except they're all running Win7 64-bit. As such, we have absolutely no idea where to start. And since most are hangs, not crashes, we can't even look at the crash reports.

So can anyone give us any idea what else we can look at? This is holding up us shipping a three-years-in-the-making major release of our software so to say this is a show-stopper would be an understatement. We've been stumped for about a month now and getting nowhere fast.

Answer 1

Found it!! Turns out there's a bug in .NET 4.0 regarding UI Automation and the changes MS introduced. Here's the info, and the fix! (Note: Even if you call MS, they will send you a link, but it's always a broken link. I managed to track this down manually.)

Note: Their article talks about a specific case that causes this behavior, but if you google around, you'll see tons of issues around hangs related to those DLLs. The latest is they're promising a fix in the .NET 4.5 runtime (from a MS post on this issue.)

Here's the KB article... http://support.microsoft.com/kb/2484841/en-us

...and here is the actual hotfix. http://archive.msdn.microsoft.com/KB2484841/Release/ProjectReleases.aspx?ReleaseId=5583

Apparently the VM didn't suffer from this. We weren't sure if the VM had the hotfix applied or not or if this only happens on non-virtualized machines. Still, this solved all of the issues and the app is now snappy again. (Man, was this fun to track down! Ugh!!)