CPU Parking (render power drops by 50%)

[cyphyr]

I haven't seen this before, CPU Parking, it seems to be related to Quad cores but I never noticed it before on my last rig (Q9450).
Half way through this evenings rendering I noticed a drop in performance and saw that my cpu resources monitor was showing my processors running at 100% but my virtual threads a 0%. On further investigation I saw that windows 7 Resource monitor saw showing them as Parked.
A second render of the same scene had all the threads working (after a re start). Nope the second render also exhibited the same behaviour.  It seems this is a "feature" enabled in Win7 as part of a power saving policy but the only way to turn it off is with a registry hack! Not something I really want to do. Dose anyone know of a safe way to turn off this feature? Is it something that would be worth (or possible) to write into a future version of Terragen. Its not a major problem for stills but for animations to loose half your render capacity could be bad news indeed.
Cheers
Richard

[Oshyan]

That's very odd, I haven't seen this problem yet. I wonder if it's something to do with non-physical cores (e.g. hyperthreading). This is on an i7, correct? Were you running Win7 on your Q9450 as well? I would think Windows wouldn't "park" a core/thread unless it was idle or something. Does changing the power scheme fix it? Does it have anything to do with Intel Speedstep or similar power saving tech?

- Oshyan

[cyphyr]

No I wasn't using Win 7 On the last Q9450, and I've only experienced this with my new system, i7920 + win7.
The screen shot above shows my second render and the parked cores seem random, but in the earlier render the parked cored were definitely the "hyper threads", cores 0, 2, 4 and 6 were at 100%, cores 1, 3, 5 and 7 were at 0%. My power saving is set to maximum performance and I cant see any changes in the advance setting that seem relevant. I've done the same scene with Ray Trace objects enabled and disabled, with the same results. This is actually the 720p scene you recommended I made last year. A whole series of smaller test renders I mad  earlier this evening did not exhibit this behaviour.
Thanks

Richard

[Oshyan]

Well, I reckon it must be an OS/software/hardware thing then. Outside the scope of TG2. I imagine you've done some searching online, due to your "needs to be changed in the registry" comment. Have you tried the reg change?

- Oshyan

[neuspadrin]

Been taking a poke around looking at it too.  Yes core parking is a "feature" of windows 7 for power saving.... something great to have enabled for server farms where decreasing cycles is handy, and something great for laptops that can shut off a core... not great for rendering

By looks of it only thing i can find is the reg edit.  It looks very safe to me as long as you do it right only editing the specific keys they mention changing that value max/min to always be 0.


The registry isn't as scary as people always seem to think it is.  Just don't screw with anything beyond what you know or are told . 

Its like the windows folder... sure you could prob add/subtract things from it in very certain cases... but don't go deleting all of it cause its taking up your harddrive space

If it aint broke, don't touch it... if it is, touch away

[Henry Blewer]

I read that the i7 chip uses adjusted threading, or something like that. It takes a look at the work load and decides how many threads to run at. The threads also jump from core to core as CPU demand increases or decreases. I wish I could remember where I read this. I think I was comparing the i5 and i7 with a Core Duo Quad Core on the Intel web site.

[jo]

Hi,

Oshyan is right that this is really a system thing rather than a TG2 thing. I've had a look for any way to programatically change the core parking settings but couldn't find anything. I will keep an eye out for anything relevant.

If you don't want to change the registry directly it looks like you can use the powercfg tool from the command prompt to change the settings. Try a search for "core parking powercfg" or there's an example here:

http://www.nullsession.com/2009/10/08/enable-cpu-core-parking/

Regards,

Jo