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Author Topic: Slow dense cloud generation with Tesla K80 GPUs  (Read 2315 times)

AndyC

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Slow dense cloud generation with Tesla K80 GPUs
« on: August 17, 2018, 12:35:56 PM »
We are encountering unexpectedly slow dense cloud generation on a high-performance cluster. Any help working out the solution would be greatly appreciated!

We have two computer systems:

Workstation: (OS Windows 64; CPU i7-7800X 6-core 3.5 GHz; GPU 1 x  NVIDIA GeForce GTX1080; RAM 128GB DDR4 2133 MHz; Photoscan-Pro 1.4.2 build 6205)

Cluster: (OS Linex; CPU 2x Intel Haswell E5-2640v3 16-core 2.6GHz; GPU 4x NVIDIA Tesla K80; RAM 256 GB DDR4; Photoscan-Pro/1.4.3)

Our test job consists of 489 x 20 MP photos, processed through the initial steps (alignment, precise markers, tie point filtering, optimisation, etc.). All available GPUs are enabled on both systems (x1 on the workstation, x4 on the cluster; either via the GUI or with "PS.app.gpu_mask = 2 ** len(PS.app.enumGPUDevices()) - 1  # activate all available GPUs"). We will be using Python scripts for (mostly) headless processing. Dense Cloud Generation was attempted at ultrahigh quality with mild depth filtering on both systems.

On the workstation, depth map generation takes 9 hours and dense cloud generation takes 28 hours (37 hours total).
On the cluster, depth map generation takes 5 hours and dense cloud generation takes >28 hours (not complete after 33 hours).

(We thought that there might be unexpected overheads with using the 4 GPUs on the cluster, but our tests with 10 and 100 image sets show processing time consistently decreases (slightly) as the number of GPUs increases).


Questions:
(1) Would anyone comment on our expectation that this Cluster should complete dense cloud processing substantially (e.g. more than 40%) faster than this Workstation?

(2) Could there be an issue with the GPU not being configured for optimal performance from PhotoScan?
(e.g. the compute mode, as hinted at by Alexey here http://www.agisoft.com/forum/index.php?topic=9199.0)


We have no experience configuring GPUs, but suggestions are welcome, especially if it might be possible to better optimise the K80s via the Python script.
 
« Last Edit: August 17, 2018, 12:47:07 PM by AndyC »

Mak11

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Re: Slow dense cloud generation with Tesla K80 GPUs
« Reply #1 on: August 17, 2018, 03:58:27 PM »
IIRC Dense Cloud generation is done entirely on the CPU while Depth Map generation is done on the CPU+GPU.

AndyC

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Re: Slow dense cloud generation with Tesla K80 GPUs
« Reply #2 on: August 20, 2018, 12:45:07 PM »
Ah, we had misunderstood that, thanks for the clarification! (there's a lot of misinformation/ confusion about this step elsewhere online)

Now that I know what to look for, there is more relevant information/confirmation at:

http://www.agisoft.com/forum/index.php?topic=8072.0
http://www.agisoft.com/forum/index.php?topic=7858.0
http://www.agisoft.com/forum/index.php?topic=8753.0

Thanks!