Laptop GPU downclocking during video playback?

[Red Hawk]

I just observed something odd on my laptop. I was playing a Youtube video in 720p in a Firefox window (hardware acceleration on), and I happened to have MSI Afterburner on. I decided I'd check just to see how much GPU usage simple video playback causes. Upon starting the video, GPU usage did spike just a bit (no more than 5% or 10%), but I was befuddled to see the clock speed drop from the stock 750 MHz to 500 MHz. Video playback wasn't effected, as video continued smooth as ever. I checked to make sure all the power settings were normal so there wasn't anything to cause it to downclock. Upon closing out of the video, the clock speed returned to 750 MHz. Is this somehow normal for a laptop GPU like the Mobility Radeon HD 5470? What might have caused it?

 

[SPBHM]

my Radeon have a specific clock for video playback (400MHz I think), another for high load (gaming) and a lower clock for low usage (desktop, idle)

the strange thing on your description is going back to 750, and not a lower clock, but a different clock for video playback is normal,

 

[Bateluer]

If the video playback is still smooth, why is this an issue? Seems like its doing exactly what it should be doing, scaling the clock frequency and power consumption based off the workload.

 

[Red Hawk]

It's not an issue, it was just curious behavior that I didn't know the cause of. SPBHM is probably right, it's odder that the GPU is holding at 750 MHz when just idling and plugged in to the wall socket. When unplugged though, it does drop to 300 MHz.

 

[zir_blazer]

The vBIOS of modern Radeons include a PowerPlay state that is what the GPU should run at if you're doing only video playback, its a middle point between lowest and highest (But not the only one). Its called UVD.