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World Community Grid Forums
Category: Active Research
Forum: OpenPandemics - COVID-19 Project
Thread: CPU usage on GPU tasks, any correlation? |
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Thread Status: Active Total posts in this thread: 6
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biini
Senior Cruncher Finland Joined: Jan 25, 2007 Post Count: 334 Status: Offline Project Badges: 
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Anybody has any insights, what's the correlation between CPU and GPU on gpu tasks?
----------------------------------------It seems, that no matter what CPU or GPU I'm using a single GPU job always uses 100% of a *CPU* core (when running nvidia or modern iGPU). Also I've found that when running a single GPU WU, it does not fully saturate a modern nvidia card (gt1030 and upwards). Could it be, that cpu cores are simply not powerfull enough to feed the GPU to keep it happy? And therefore, is it possible to occupy 2 CPU cores on one GPU wu? Random observations on fast nvidia cards and AMD Ryzen; 4 simultaneous GPU WUs will fully saturate the GPU fully and my cpu will use 4 cores (~33% cpu usage). 8 simultaneous GPU WUs will fully saturate the GPU fully and my cpu will use 8 cores (~66% cpu usage). 12 simultaneous GPU WUs will fully saturate the GPU fully and my cpu will use 12 cores (~100% cpu usage). So if the GPU usage stays the same, why does the CPU usage go up? I have dedicated SAS-controllers for my disks, so increased writes on disk should not be an issue. Also, it seems that AMD/ATI cards wont use CPU at all. |
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ca05065
Senior Cruncher Joined: Dec 4, 2007 Post Count: 326 Status: Offline Project Badges: 
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The explanations I have seen offered before is that Nvidia has its own proprietary GPU language CUDA. They have made it very efficient but it only runs on Nvidia hardware.
World Community Grid wants to include as many participants as possible so opts to run projects using OpenCL language which runs on most hardware. OpenCL has been implemented differently by the manufacturers: With an AMD GPU, the CPU part of the program appears to pass work and control to the AMD GPU and then does nothing until the GPU needs the CPU do perform some work. With a Nvidia GPU, the CPU part of the program appears to pass work and control to the AMD GPU and then keep asking the GPU if the CPU needs to perform any work for it which accounts for the high CPU usage. |
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maeax
Advanced Cruncher Joined: May 2, 2007 Post Count: 142 Status: Offline Project Badges: 
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0.25 CPU and 0.25 GPU for a AMD Radeon WX7100.
----------------------------------------Yesterday got GPU-Work for 4 Tasks parallel. The most time in the past only one GPU-Task. This is ok, because we have no Stresstest atm.
AMD Ryzen Threadripper PRO 3995WX 64-Cores/ AMD Radeon (TM) Pro W6600. OS Win11pro
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flynryan
Senior Cruncher United States Joined: Aug 15, 2006 Post Count: 235 Status: Offline Project Badges: 
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1 CPU for each GPU task is what I do. Don't want anything holding the GPU's back.
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biini
Senior Cruncher Finland Joined: Jan 25, 2007 Post Count: 334 Status: Offline Project Badges:
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Thanks ca05065, that makes sense
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gordonbb
Cruncher Canada Joined: May 14, 2019 Post Count: 19 Status: Offline Project Badges:
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The Nvidia driver has a Spin Lock on it so any CPU thread assigned to a GPU will show 100% in use though the load on the CPU is less as the thread is locked to the driver. The AMD driver does not have an exclusive lock on the CPU thread feeding it so often one can drive many AMD GPUs from one CPU thread.
----------------------------------------This is why, as some have observed, that equivalent GPU tasks running on a NVidia GPU will show higher CPU usage, an thus more run-time towards badges, than the equivalent task running on an AMD GPU. My personal observation with NVidia GPUs is that for NVidia Pascal you can run 4 tasks or more on 1070 and higher GPUs and lesser GPUs should run 3 or less. For Turing the 3/4 split seems to be a 2060 or 2060 Super.  AMD - 2600x, 2 x 2700, 2700x, 3900x, 3950x, 2 x 5900x, 5950x Intel - E3-1231v3, 9900K NVidia - GTX 1060 6GB, 1660ti, 1070ti; RTX 2060, 2060s, 2070a, 5 x 2070s [Edit 1 times, last edit by gordonbb at Jul 29, 2021 9:34:14 PM] |
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