Huge power discrepancy between IGP and Discrete video

[Metaluna]

I've recently built an HTPC primarily for running XBMC under Windows 7, but also for occasional Bluray playback. I am using an older Socket 1156 H55 motherboard (Gigabyte GAH55M-USB3) and a Clarkdale i3-540 processor with integrated IGP (Intel HD 3000 I think).

To make a long story short, I am seeing a much higher than expected jump in both idle and video playback power consumption between an IGP-only system, and the exact same system with a discrete video card, and I can't figure out where the extra power is going.

With the IGP only, the system idles at around 45W. Playing a typical video with XBMC only seems to add a couple of watts. But when I plug in a Radeon HD 6770, the idle power skyrockets to around 85W. That's a 40W jump (using the latest Win7 Catalyst x64 drivers from Jan 2012). Again, not much difference between idle and playback power consumption, so I don't think it has anything to do with the video decoding load.

I was under the impression that the 5770/6770 generation of video cards had idle power in the 15W ballpark. Figuring in 5W or so for PSU inefficiency (Antec Earthwatts 380) and general Kill-A-Watt inaccuracy, that leaves at least 20W unaccounted for. Is this normal for an H55/Clarkdale system? Is the mere presence of an external video card perhaps causing some other part of the CPU/motherboard to come awake and consume large amounts of power? Maybe something in the southbridge? Would a Sandy Bridge do better here?

Unfortunately (or perhaps fortunately) I had to return the 6770 which was a loaner from a friend, but I do have a new Sapphire 7750 card on order. I'm hoping that one fares better but it seems like something else in the system is dominating the power consumption.

[MikeC]

Which version of XBMC are you using? I've tried various versions -- the earlier ones always had high GPU loading. Too high for low power usage, imo. The latest, 11 (in various revs), has much lower GPU load & is considerably faster in general. You should check idle power in Windows and playing the same videos with something like Media Player Classic & compare with XBMC numbers.

With a Phenom2 quadcore, I get ~40W idle in XBMC. typically 10W higher playing HD video.

[Metaluna]

I'm using XBMC 11 (Eden) RC2. Unfortunately I no longer have the 6770 to test, but shortly after posting, my new Sapphire 7750 arrived a day early, so I'm testing it now.

It looks like things have vastly improved. Using the latest Catalyst drivers (which I had to download from Sapphire, because the 12.2 drivers at AMD's site don't recognize this card for some reason, even though they're supposed to add support for the 7000 series), I get a Win7 desktop idle power of around 52-53W, so the card adds about 7W idle power compared to just the IGP.

Running Furmark 1080p, I peak at around 101W.


Using Windows Media Player, and playing the sample video at: C:\Users\Public\Videos\Sample Videos\Wildlife.wmv:

67W



XBMC 11 RC2, playing from a network share:

C:\Users\Public\Videos\Sample Videos\Wildlife.wmv: 65W
Ripped Bluray ISO (1080p): 68W
Xvid-encoded 720p .mkv: 64W


So it looks like my system is back to sanity. Something must have been weird about that 6770, or the video driver.