So for giggles, I was running DPC Lat on Win 7 DAW.
 
With nothing running I was getting ambient latency of ~150 microsecs and the occasional spike at 300-350.
With Sonar or iTunes running I was getting the same sort of latency.
 
However, if I left DPC Latency Checker on when shutting down Sonar or iTunes (i.e. nothing running again) my latecy would spike to 14,000 microsecs (big ugly tall red bars.)  If I fired up the software again, the latency went back down to prior levels.  If I opened up the audio interface utility, the latency would go back down to prior levels.
 
Anybody seen this before?  It is not contributing to a performance issue, but it seems really strange that the latency would sky rocket when exiting audio software.

Hi Dave,
 
CPU throttling can cause such issues.
You can go into the motherboard's BIOS and disable these features.
 

I've noticed it and always assumed it was a bug with the latency checker.  Just restarting the latency checker is unlikely to change actual DPC latency.

The DPC latency checker program isn't really a very good program at what it does. Better to have a look at LatencyMon. More complex and reports on more things, but far more accurate and useful. Also works right in Windows 8.

Sycraft
The DPC latency checker program isn't really a very good program at what it does. Better to have a look at LatencyMon. More complex and reports on more things, but far more accurate and useful. Also works right in Windows 8.

 
The DPC Latency Checker doesn't give any information about what is specifically causing high DPC Latency, but it is accurate under Win7x64.
 
The OP's DPC Latency can be reduced by changing settings in the BIOS.
 
Also, the OP should check to see if anything significant is running in the background (like backup software scheduling services, etc).

I've used both.  The DPC Latency Checker is good to get a quick feel of the system or if it has a problem. 
 
The Resplendence Latency Monitor goes deep into the system and provides a lot of data, but I can't figure out what the hell its telling me.

Just to note, I am not experiencing any issues.  I thought it was odd that when running Sonar (and prior to running any software) latency was in the 180 microsec range, but when Sonar was stopped (or iTunes for that matter) latency spiked.  When I fired up Sonar again it returned to the low levels.
 
Again, I don't experience any issues when running Sonar, so I am inclined not to change anything, but I observed something strange (to me) and wanted to report it.

Most likely, it's because of CPU throttling.
When the CPU is throttled up to full speed, DPC Latency is lower.
You can disable CPU throttling...

It's to bad the DPCLAT latency monitor doesn't work in Windows 8. You see that it gives a false reading of 1,000 ms steady. 
 I have always kept it on my desktop. I would randomly check whats going on. For my live performance XP laptop it was indispensable as it would tell me it's time to clean things up or remind me I left the battery managment or wireless on. 
 
I too like fireberd have yet to totally decipher Latency Monitor. I am using it on my new W8.1 DAW now. That Hard Paging bar graph just keeps growing as time goes by, but it still tells me everything is OK. I think the other bars are telling me I'm under 100ms so all seems fine. 
 
 
An interesting ( to some?)  note on running DPCLAT latency checker. As an experiment once I thought I'd run it as I re installed a fresh OS and software. This was a 2004 Acer Laptop. 
The first thing I did once Windows XP 32 bit booted was run the DPCLAT.  
Processes running 23. 
It was under 50ms and steady. 
OK, installed the chipset, wi Lan, Lan and video drivers. Hmm, up to 400ms? 
Disabled battery management, back to 100ms 
Disable Wi Fi back to 50 ms. 
Note nothing else was changed from windows default install. 
Processes running 26
As I continued to install software I'd leave it running and start it again after re boots
Lots of red and orange Spikes now but of course that's normal when ever you use the CPU. 
But when idle it stayed steady at 50-80 ms. 
Here's the weird one and if you dig way back in the hardware forum you'll see my screen shots. 
 
Installed my Tascam us1641 drivers and now we are up around 200 ms?? 
Turn off the Tascam back to 50ms? 
What was interesting is this was the behavior on all XP computers. On windows 7 64 bit it only would go up about 20-40 ms. 
 
So to the OP, you can expect a change in the DPCLAT readings as you open and close programs. This is why it's a good idea to test your DPC latency while running your DAW. 

Poorly written drivers can raise DPC Latency (common with video drivers, WiFi, etc).
CPU throttling was also happening with your laptop (causing changes to DPC Latency).