dual core only 50% load while rendering

What do I have to do to use the full 100% power of my Dual Core CPU? I am rendering out a softbody animation, but my CPU never goes over 50% (Windows XP). I use the blender internal renderer with Threads toggled on. Is there something else I have to setup? I tried Yafray which is multithreaded, I chose 2 CPU´s, but it made blender crash. Maybe because I am using the lastest CVS build.
Thanks in advance for any hints!

For blender internal press the Threads button in the render panel,


That is what I have done, but as I said, only 50% CPU load.

Gruß Gott!

are you seeing the 50% load while the softbodies are calculating?
this is expected as that portion of blender is not multi-threaded(yet).

if when you render you are only using 50% you have a problem with your os?

I see the 50% while rendering (F12, or Do ANIM-Button). I am aware that the calculation of Softbody (ALT-A) is happening in the blender thread. But I read somewhere that rendering should work multithreaded.
My OS seems okay, I am running Windows XP Professional SP2.

not all of the rendering pipeline in multithreaded I think, but not sure which specific features are not. Try baking the softbody first, to ensure that isn’t it.


I baked the softbody and then I rendered the Animation again (ANIM). The rendering went faster (of course), but still with only 50%.

Do you have hyperthreading enabled?

Thanks for the links. I looked through all settings in my BIOS but there is nothing about hyperthreading. Obviously Dual Core doesn´t need that to use 2 processors simultaneously? After all, this is a Dell Notebook Inspiron 9400. I checked again the system monitor and if I do a long render, the CPU usage will vary between 50-55%, sometimes a peak of 60%. I don´t know what to do!?

I suppose you have two cores and hyperthreading enabled, thus 4 virtual processors. If you hover mouse over the Threads button in Render panel, the tooltip says Blender renders only in two threads. So 2 of your virtual processors are doing nothing.

That of course is not a bad thing. The 2 other processors are only virtual and using them would require massive context switching on the processor. Look in your motherboard manual how to switch HT off (or contant the manufacturer) to check if there is a speedup.

I don’t have any experience with HT, but from the couple of articles I read, I understand, that sometimes you need to reinstall processor drivers or the OS itself after HT switching :).

Try disabling the threads in blender and check if your load will be 25%.

And last thing - Windows XP is HT aware, so it uses one virtual processor from each core (and not two virtual processors from one real core, what sometimes happens in Win2000), so I don’t think there will be much performance gain by switching HT off.

You are right, and thank you very much for your answer! If I switch “Threads” in Blender off, I only get a cpu load around 25-30%. So it seems all this excitement about dual or even quad core processors is vain at least when it comes to blender and fast rendering times? So the best processor for blender would be a turbo fast single core with hyperthreading, yes?

Dual AMD 64 or Dual Core Duo are your best bets in the near term.

If you want more than dual core you need to compile it yourself (it is hardcoded to a max of 2 now, because some things have issues still at more than 2, although people have had perfectly fine performance on quad cores, and blender was even ported to a super computer but that required some changes…).


well, i am not so deep into this that I could compile blender for more threads. I tried to open blender twice and started a long rendering process in each, and finally I got my 100% processor load!:slight_smile: Maybe I just have to change my habbits and work in two sessions!

It would be cool if there was some sort of script that would start another process from the commandline as soon as you start a rendering, and the other process could render every other frame…that could also work for a quad core (with 8 threads?)…