What is the CPU doing?

Amongst bloggers there is a contest to see who has the longest interval between posts and as you seen I entered that contest. I won’t even apologize. My last blog was about FSX and why we have so much problems running it. Basically I said the users were behind on hardware but I now realize that’s not true. Let’s see facts as they are, FSX has problems. Serious problems.

No matter what Microsoft tells us (not that they tell us a lot), if we see exactly the same and do exactly the same in FSX and in FS2004, we see half the frames in FSX. So MS told us to start using the special FSX code and different tools and we did. We got better looking objects but even lower framerates because there was more calculation to be done on every visible polygon (the shape that makes up the things you see). Now this is new.

In the past we were used to see a drop in framerate in the default simulator with every update, but per polygon we always had the same framerate. The default sim would look better and that costs frames, but with the same objects loaded we had similar framerates. Not so in FSX, even if we dress FSX down to use FS2004 aircraft and FS2004 scenery we get half the frames. And that CPU power is not used for better flight dynamics, better weather or better ATC, because as we all know, that is simply not there. So we lost half the frames and gotten basically nothing in return.

In fact things are even worse. One of the big steps forward was supposed to be the better use of the GPU (graphics card) power. If you have a modern GPU you got a little computer there that might be as powerful as you main CPU! Using Direct X the software can send a ‘object’ (say a cube), a texture (say wood texture) and a light source (say the sun) to the graphics pipeline and your GPU will put the texture on the object and calculate how the light will affect it, create shadows etc. Your CPU is at that time free to do other things. In FS2004 the CPU had to do a lot of these things but in FSX it is supposed to be DirectX and the GPU who handles a lot of that. And to a certain degree that is true, updating your graphics card for FS2004 could make it look better but hardly mattered for your frames. In FSX a fast graphics card does make things faster and looking better. But it is well know that FSX is still basically CPU limited. Your FPS depends on a lot of things but the speed of your CPU determines at least 80% of it.

So we lost half the frames and the CPU is supposed to have less to do. What is that CPU doing? We can look at processes that are running and we see for example a very strange amount of disk handling (some files are loaded dozens of times in a matter of seconds). We also see the expected huge amount of I/O with the graphics system. But per polygon FSX is just a whole load less efficient.

So what is the CPU doing?