CPU low usage on 64-bit XPlane: symptom and cure

[Emerson67 248]

Along the 10.20 beta versions, i've noticed that x-plane 64-bit process has been far from using 100% CPU time, while there's no other system bottleneck. This behavior has been confirmed by other users on LM blog.

 

On my PC, XP 64-bit uses about 70% CPU time after sim startup, and stays at this level indefinitely, UNLESS:

 

- I start a weather change event...

 

like: setting something different on the static global weather, reloading real weather from the net, etc.

 

Then the CPU will go to 99.99% load and will stay at this level, giving a FPS boost until the end of the simulation session.

 

In my case, I always got about 30% FPS increase

 

BTW, i filled a bug report to Laminar.

[carrotroot 77]

This is normal behavior for X-Plane, your CPU shouldn't be pegged at 100% all the time. Since some of the rendering is off-loaded to the graphics card this frees up some of the CPU's resources.

[FloB 34]

What is this about? Unless you checked how the "load" is spread over your cores it's not a "bug".

E.g. X-Plane tells me the CPU load is 40% whilst the windows task-manager shows that one core is almost maxed out and three cores are within 20% max. load. Everything is fine here, right?

 

Cheers

Flo

[Emerson67 248]

Pay attention to this:

 

At XPlane startup, CPU is at "0.74" (i.e. 74%) load and FPS is at 24. These are XPlane OSD readings. It will stay at this condition unless you trigger the "magic event". :smile:

 

At this point, someone may think that the bottleneck is outside the CPU, but if you check de GPU load, you find no bottleneck.

 

Now, doing the "magic trick" described above, the FPS goes to 36, while CPU load goes to "0.99" (99%). Now all CPU cores are at 100% load.

 

I went from 24FPS to 36FPS. An 50% performance improvement.

 

In my testings, XP stays at this CPU usage profile along all the simulator session.

 

Detail: my graphic settings on XP are maxed-out (most of them). 1920x1200x32. See "My PC" on the left.

[carrotroot 77]

I don't see what the issue is here. The CPU should remain mostly idle when it's not doing some sort of I/O proceedure such as scenery loading. As for your frame rate change it's more likely that the introduction of clouds has decreased the visibility range which would have a noticeable change in the frame rate.

[FloB 34]

Now all CPU cores are at 100% load.

...

In my testings, XP stays at this CPU usage profile along all the simulator session.

 

 

Get ready to buy a new CPU soon

Already smell some smoke...

 

Cheers

[Emerson67 248]

Is not the clouds. Unnaturally, if I add a cloud layer, I get a FPS boost (24 to 36). If I remove the same cloud layer, instead of returning to 24, it stays at 36. The bug is very consistent and reproductible 100% of the times, on different computers. You must have AI off to avoid it masking the bug. In addition, use a stock plane to avoid masking, because 3rd-party planes may use multithreading code.

 

Other users have reported the same issue. An important info: the issue happens on 64-bit 10.20 xp only. Other users reported the same.

 

I don't see what the issue is here. The CPU should remain mostly idle when it's not doing some sort of I/O proceedure such as scenery loading. As for your frame rate change it's more likely that the introduction of clouds has decreased the visibility range which would have a noticeable change in the frame rate.

[Longranger 148]

Other users have reported the same issue. An important info: the issue happens on 64-bit 10.20 xp only. Other users reported the same.

Not unusual. X-Plane 10 is heavy on memory transfers. The CPU and the GPU can be far under 100% when the computer simply runs into a bgandwith bottleneck, and the 64 bit version uses some 64 bit pointers which can mean that some components have to make 2 transfers instead of one. But there is simply no system that shows you precisely where in your computer the transfer problem occurs (such values would mean additional transfers...).

[FloB 34]

I can't reproduce the said behavior on my system. CPU load (in XP and windows taskmanager) is not affected by loading or reloading the weather. No significant FPS-change either.

 

By the way: I've never seen XP10 use all cores to full extend (i7 2600k here). Usally it uses one core at 70-100% and the others between 10% and 50%. Especially if you don't use AI traffic a permanent CPU-load of >90% for all cores is unreasonable in any way and not a sign of efficency.

 

Cheers

Flo

[Emerson67 248]

OK, I have 2 news to kill this topic:

 

1) My late finding: the "in-game" CPU load reading (OSD) is fully unreliable. When it shows "0.995" for example, the actual CPU load is sometimes 40%, sometimes 60%, etc.

 

2) I've upgraded the NVIDIA video driver to 314.07 and could not reproduce the FPS gain behavior.

[Delta Captain 0]

I'm very worried! My cpu usage stays at 30% and gpu usage stays at 50% all the time! There is something wrong here!

[carrotroot 77]

I'm very worried! My cpu usage stays at 30% and gpu usage stays at 50% all the time! There is something wrong here!

 

Please explain why do you think having a low to moderate CPU/GPU load this is a bad thing?  

Edited February 25, 2014 by carrotroot

[gheeD 62]

I also noticed that after someone here on avsim forums said it, that the cpu load seems to often be somehow both cpu + gpu load. After reading i tried it, and sure enough often times cpu load 0.991 for example id be hoovering around 30-40% cpu load and 70+ gpu load. So i wouldn't really trust the ingame monitor for it, rather nowadays i use afterburner and windows task manager for gpu load + memory usage and cpu load on my 2nd monitor.

[Humpty 751]

Here it is
 

http://forum.avsim.net/topic/435015-nvidia-gtx770-4gb-or-780-3gb/

 

 

I use coretemp for CPU loads.

[Delta Captain 0]

Please explain why do you think having a low to moderate CPU/GPU load this is a bad thing?  

Because it means I have no bottleneck, and also my vram usage is 1300-1400 mb (I have a 2gb card) so I know that a full frame buffer is not the problem, and therefore most of my computer is sitting there with half of its potential being wasted for no reason! Please explain if i'm missing something. Is this an amd bug possibly?