Learning Forum

[Mahdi Ben Ftima]

Hello,

I'm trying to run a DEM-SPH analysis on Rocky using mutiple-GPUs. I have a workstation with 2 gpus (RTX A6000 with Nvlink) I noticed performance problems when using multiple GPUS. The analysis runs more rapidly with one GPU ! Also, when I use the GPU information with Rocky, I got the follwoing status: 

Is GPU Capable P2P: False

[Lucas Bertollo Baggio]

Hello Mahdi, 

 

In simple cases (with few particles and triangles, for example) it is normal to lose some performance with Multi GPU. Furthermore, Rocky does not use P2P anymore, so you can dismiss this status warning. 

 

Feel free to continue this conversation here,

Kind regards,

Lucas

[Mahdi Ben Ftima]

Hello Lucas and thanks for your answer. Precisely, I'm running complex analyses involving more than 10 millions of SPHs and thousands of DEM particles. One analysis can last more than one week. Additionally, since P2P is no more used by Rocky, does this mean that the physical Nvlink is not really required ? This is not the information I got from this video session  posted by Rocky four years ago: https://www.nvidia.com/en-us/on-demand/session/gtcfall20-a22210/

[Lucas Bertollo Baggio]

Hello Mahdi, 

 

in order to better understand your case, you can open a ticket for the support team to help you. Additionally, using Nvlink is still beneficial because it speeds up the information trading between the GPUs.

 

kind regards,

Lucas 

[Mahdi Ben Ftima]

Hello Lucas,

I'm not sure if I can open a ticket for the support team, since I'm paying for an academic license of ANSYS/ROCKY. 

[Lucas Bertollo Baggio]

Mahdi,

in this case you could might check the GPU Buying Guide, available here in AIS, for more GPU usage information in Rocky.

[Mahdi Ben Ftima]

Hello Lucas, I explored the guide before buying workstations. Actually, I have two workstations: one with two GPUs RTX4090 without Nvlink (that was my first trial) and another one with two RTX A6000 with Nvlink. Strangely, the one without Nvlink is running faster for our DEM-SPH models because RTX4090 have better perfromances than RTX A6000 (while being cheaper than A6000, because it is a gaming card without possibility). With more hindsight, I don't think the Rocky software is optimized for parallel multi-GPU computing for cases involving SPH analyses. I feel like I made a bad investment in the software and also in the workstations... Thank you anyway for your help, but it's clear that without support, I won't be able to advance further in my research. 

[Lucas Bertollo Baggio]

Hi Mahdi,

The RTX4090 has better performances than A6000, so it should run faster. The NV-link has not been tested in any benchmark so far. We cannot conclude about its benefits, but it might have marginal gains.