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giugio

DX11 dx 11 and multicore cpu

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Hello.
I read some documentation on intel tbb.
From what I understand the generation of the tasks and their execution with the task sheduler is very useful for application logic (in my case a game).
I was wondering if you can use the tasks and sheduler for rendering operations in dx 11.
Somewhere (I seem to recall an example of the last directx 11 right in the SDK) there is an example that explain how speed up the rendering with multicore.
Where i can find some documentation ?
In google there are a lot of articles but not tecnical articles in c++ and dx11
thanks.

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I suppose any tutorial on multithreading will do.

That's about what we get with advancement on core number and simultaneous thread execution.
It's not a DX11 thing really, AFAIK DX11 doesn't care whether your cpu is qualcomm or intel, single or multipcore - Pleas correct me if i'm wrong.

If you want totorials of how to split up repeating DX processes, I think you can look at about anything related to graphics and multithreading. Check the graphics card pipeline and get a feeling of what things are thread safe and not.

For instance, having a geometry generator or texture loader could easily take place in a seperate thread without crashing a DX application.

But I'm rambling. Maybe that's not really what you wanted to know.

[Edited by - SuperVGA on November 30, 2010 6:57:23 AM]

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Direct3D 11 natively supports multithreading, and allows for multithreaded resource creation as well as multithreaded command list creation. The latter point is more interesting for performance, and could significantly reduce the amount of CPU overhead involved with submitting all of the API calls.

There is a sample in the DXSDK that shows how to implement the multithreaded command list generation. The Hieroglyph 3 engine also implements multithreading, so you can take a look at that too.

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Any insight into when using multithreaded command list generation is beneficial? When I run the SDK sample, it takes a few extra milliseconds when using the multithreaded paths, despite taking extra CPU time (which i suppose means its actually multithreaded at least haha)

I assume it must have something to do with the length of the command lists..

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Any insight into when using multithreaded command list generation is beneficial? When I run the SDK sample, it takes a few extra milliseconds when using the multithreaded paths, despite taking extra CPU time (which i suppose means its actually multithreaded at least haha)

I assume it must have something to do with the length of the command lists..

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It does indeed have to do with the size of the command lists, and it also depends on how many cores you have on your machine. If you run it on a single or dual core machine, then it may not help at all (and may actually decrease performance as well).

If your app is CPU bound though, it could be quite beneficial to parallelize the CPU submission calls. I don't have any hard numbers, but I have been developing some stress tests to see if I can find where it starts to benefit from having the multiple cores. Hopefully within the next couple weeks I will be able to add the stress test to my engine distribution...

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The main "problem" right now is that while drivers support multi-threaded resource creation they (when I last checked) didn't natively support multi-threaded command list creation.

So, the runtime and driver kind of 'fake' it right now (effectively storing everything up and then submitting as normal); although I think we are getting closer to native support for this functionality.

The main point being that, atm, any stress test won't give an accurate view of how things will work in the future [smile]

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The 'Driver Command Lists' ability reported by the runtime is based on the driver's ability to simultaneously create command lists from multiple threads. However, the benefit from multithreading can still be had depending on how much work is done to generate a rendering sequence. For example, if the transformation matrix concatenation is performed on each thread for independent rendering passes, then the net result is to divide the number of transforms needed to perform by the number of cores on the machine (neglecting memory access pattern effects). This will still have a positive effect on performance, regardless of if the command list is created in parallel or in sequential operation.

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Out of curiosity, I just ran the multithreaded rendering sample from the SDK on both my laptop and my desktop. Here are the configurations and the results:

Laptop: Core 2 Duo 1.6 GHz, 2 GB, Vista, 8600M GT - Single threaded ~5-6 FPS, Multi-threaded ~8-9 FPS
Desktop: Phenom II X4 3.2 GHz, 4 GB, Win7, 5700 series Radeon - Single threaded ~22-24 FPS, Multi-threaded ~44-45 FPS

So in both cases I see a significant speedup with the MT activated. Also interesting is the fact that the laptop GPU is a DX10 part, meaning that the CPU savings are implemented with a DX10 driver for the DX11 runtime. I suspect that if you see degraded performance in this sample, you are probably GPU bound meaning that the parallelism can't help you anyways...

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Hmm interesting. I updated my GPU drivers just now and it has improved performance of the multithreaded path. Immediate mode appears to be the fastest, so like you said I must be GPU bound

Desktop: i7 3.4 GHz, 64-bit win7, HD5750

Immidiate ~65 fps
ST Def/Scene ~39 fps
MT Def/Scene ~54 fps
ST Def/Chunk ~50 fps
MT Def/Chunk ~55 fps

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