Select a GPU to be used by a function running in parallel(parfeval)

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Tutu 2019-8-16

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评论： Tutu 2019-8-21

Hello,

I am using two GPUs in a GUI postprocessing images live.

I am using the 'FramesAcquiredFcn' as a hub to transfer data from the buffer to the CPU RAM memory ('getdata') and launch a 'parfeval' function on GPU postprocessing these data. I have 1 pool with 3 workers initialized (one for the 'FramesAcquiredFcn' and one for each GPU). I can check that when the 'parfeval' function is not finished at the next iteration the second GPU is used instead. Now, I know that using 'wait' I can force the first GPU to be used.

However, I would like to split my postprocessing between these two GPUs because one is more powerful than the other. Hence, I would need the first 'parfeval' function to use the GPU1 pass the outputs (using 'afterEach'?) to an other parfeval function using the GPU2.

I have read the 'help selectGPU' but could not figure out how to modify it for my purpose.

Any help will be welcome.

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Answer 1

Joss Knight 2019-8-18

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I'd have to know what kind of postprocessing you're doing - please post some code. On the face of it, the answer is simply to use gpuDevice(i) to select a particular device for each of your parfeval calls.

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Tutu 2019-8-19

Hi Joss Knight,

The issue I have with gpuDevice(i) is that it takes typically more than 1s to be executed, and I need to run the application live; tic;gpuDevice(2);wait(gpuDevice);toc;tic;gpuDevice(1);wait(gpuDevice);toc; gives me 1.6 and 0.95 s, respectively. Hence, using it would considerably impede what I am doing; as in this amount of time, I would queue much more data and saturate my memory even more rapidly.

I am looking for a way to initialize a GPU to be used by a worker, and use this worker for a parallel.FevalFuture.

Typically, my first postprocessing on GPU consists to fft2 1920*1220*100 (single), cropped out an area giving me 1920/6*1220/6*100 (single) which is ifft2 and divided my a 1920/6*1220/6 (single) preloaded on GPU. Then fft2, cropped to 1920/(6*2)*1220/(6*2)*100 (single), fft along the third dimension, cropped to 1920/(6*2)*1220/(6*2)*50 (single), reshapped, and ordered following the histogram principle.

The second postprocessing consists of few fft on small matrices.

If really necessary, I will provide some code.

Joss Knight 2019-8-21

You can use a third-party scheduler and give it the properties you like, but I suspect that is not really what you're after. I think the real issue here is that MATLAB has no way to switch devices without resetting the device, which is slow; this is something we intend to improve.

You may be able to use client/worker parallelism here. Do your front-end work on the client on one GPU and dispatch your background work to a single worker that has the other GPU selected (or multiple GPUs all of which have the other GPU selected, if that's appropriate).

Tutu 2019-8-21

Thanks Joss Knight for your answer. It is not what I am after, but I understand as well that MATLAB has not yet implemented this option without reseting the whole device. It is what I needed to know.

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Select a GPU to be used by a function running in parallel(parfeval)

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