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Blakeman

Low CPU & GPU use but low FPS?

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Am I missing something? What could be bottle-necking me here?

At a regional airport with not much scenery and modest graphics settings.
CPU: i7 5820K

GPU: 2 x GTX 970s in SLI

bottleneck.jpg

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Although I don't have SLI, it is my understanding that SLI doesn't work well in X-Plane.  I'm sure someone else has a more knowledgeable answer to this.

 

Short of taking out one card and trying it, I know of no other answer. 

 

John


John Wingold

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You have twelve cores. If the CPU load is at 12, this indicates that one thread is maxing your CPU.

So, it seems that the most demanding thread in X-Plane is limiting your performance on your CPU.

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And that single thread has been spread over 8 threads? Is X-Plane not multi-core/thread friendly?

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And that single thread has been spread over 8 threads? Is X-Plane not multi-core/thread friendly?

Yes, that's usually the case. Windows changes the core for execution of a thread many times per second. That's the reason why you see the distribution of the load to several cores. I agree that this is misleading in the task manager visualization, but in most cases, there is one very demanding X-Plane thread involved that's the bottleneck.

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Alright - any idea how to track down what's causing it? Pretty frustrating to get super low performance like this and have bugger all of my PC's power get used.
As a side note, looking at something like the roof of the aircraft causes my FPS to jump to around 40... which is why I thought it might be graphics related.

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Another thing you might want to watch is GPU load.  It is my understanding (and Andy or others who are programmers step in here if I'm off base) that you need to keep your total VRAM load below the maximum VRAM of your video card (not cards).  Apparently the GPU loads graphics and expands them 2X or 4X to manipulate them for the AA and AF settings, then downsizes them and sends them to the monitor.  If you run over the maximum VRAM, the GPU swaps data into and out of system RAM which slows the process tremendously. 

 

I've said this before many times (thanks to Andy) - get a copy of GPU-Z (freeware on the internet) and monitor the total amount of VRAM being used by your system.  It will be almost twice what the Rendering windows shows at the bottom.  If you are running over VRAM limits, pull back on some of your Rendering settings until you bring it below VRAM max.  You might want to do this in the area of some complex custom scenery and HD or UHD mesh if you're running that.

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Go into your settings page and see what the amount of VRAM is used at the bottom of the page. Remember SLI video memory is not additive so if you have 2- 2GB cards you still only have 2GB available not 4GB. Iv'e seen XPX gobble up all 6 GB on my Titan so the post above is probably what your running into. Try turning on texture compression and lowering your AA to 2x or so if your using HDR.

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Remember that in spite of recent strides, X-Plane is still mostly dependent on a single CPU for most stuff. This includes a lot of things that you would instintively believe is the job of the GPU, like displaying objects, shadows, reflections, clouds, traffic, etc.

 

I have recently exchanged my GTX770 for a GTX850 and have not gained a single FPS in a controlled comparison scenario.

 

Show us a screenshot of your rendering settings and one with the scene displayed (no debug windows) - plus tell us the location you are at and the third-party scenery you have installed (if any) for us to make an educated guess if what you see is plausible.

 

Jan

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I have a single GTX 970, and an i7 4790 4.7GHZ CPU. 

 

I'm getting well over 100FPS on my 4K monitor at Heathrow with ultra/high settings. (This is because there is no need for Anti-aliasing at 4k resolution, so turning this off makes no difference in picture quality, but gives an instant 30-50FPS depending on my location).

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I have a single GTX 970, and an i7 4790 4.7GHZ CPU. 

 

I'm getting well over 100FPS on my 4K monitor at Heathrow with ultra/high settings. (This is because there is no need for Anti-aliasing at 4k resolution, so turning this off makes no difference in picture quality, but gives an instant 30-50FPS depending on my location).

Hmm. I sort of disagree. I'm also on 4K and everything looks fine with no anti-aliasing when nothing is moving but as soon as you get up to altitude, lines in the distance, shadows, water reflections etc. all need anti aliasing or they look like garbage to my eyes. 

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I agree with @Slayer EXCEPT that you cannot rely on the numbers at the bottom of the Rendering window to know exactly what the VRAM load really is.  GPU-Z is free on the internet (Google it) and it will show about TWICE what the rendering window shows.  Do not go by the Rendering window numbers.

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Well my cards have 3.5GB of fast memory each, and 500mb of slow memory, so as long as I stay under 3.5GB, I should be fine. In game my VRAM use is well under 1.5GB. I'll check it with GPU-Z and report back.

 

EDIT: Still only getting ~14 FPS with GPU-Z reporting my VRAM usage to be well under 3GBs

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Alright, so to test things further, I went to a really remote airport with little to no building data in X-Plane. YPKA - Karratha, Australia.

GPU usage is around 25% on each... should be able to reach 50% on each if X-Plane is not SLI friendly. If it is, then 100%.

CPU total usage is about 9%. Highest usage on a single thread is about 40%, rest have very little usage, around 5%.

FPS is about 28, which in my opinion is dismal for how little it has to render. I'm sure you'll agree when you see my settings;

NOTE: I am not actually running 5760 x 1080 at the moment, only 1920 x 1080 in windowed mode.
settings.jpg

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FPS is about 28, which in my opinion is dismal for how little it has to render.

 

You won't find a good solution by this way, since the CPU and GPU meters are to general to show the real bottlenecks. The main reason why they use these meters at all: They add a rather low overhead. To find the real bottlenecks is much more complicated. and not really useable in a game. Instead you start with low settings and increase element by element, till you have a decent combination. You could probably increase many settings without any fps since many settings work rather well independend of each other. But you should probably lower the distance and the water reflection detail a bit. These are probably the settings that limits your setup at the moment. In fact water reflection details are normally best in the third or fourth lowest settings. The higher settings don't hav really better quality but they can have a rather big effect on the fps (depends on the environment). But you should activate HDR, increase the number of objects and so on, YOu have normally one or two settings that trigger bottlenecks and it doesn't help any one to decrease other settings.

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