Are we sure CPUs don't bottleneck GPUs in FAH?

jebo_4jc

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I'm watching my GTX 1080 completely consume a core of my Ryzen 5 3600, and I'm thinking, I've been seeing this same behavior for years. It seems like every GPU has always taken 100% of a full CPU core of every CPU I've owned. Has anybody benchmarked CPU speed to see if CPU speed could bottleneck the GPU at all?
 

Icecold

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I'm watching my GTX 1080 completely consume a core of my Ryzen 5 3600, and I'm thinking, I've been seeing this same behavior for years. It seems like every GPU has always taken 100% of a full CPU core of every CPU I've owned. Has anybody benchmarked CPU speed to see if CPU speed could bottleneck the GPU at all?

I would be surprised if 3600 core bottlenecks a 1080, but I definitely know that slower CPU's than a 3600 can. I've paired low end CPU's with higher end GPU's several times, and have had poor FAH performance compared to a faster CPU paired with the same card, but most BOINC projects have ran fine with the lower end CPU. Mind you my 'low end CPU' could be something way unevenly matched like a Core2Duo or Phenom II or something with a fast GPU. Linux seems to do better with this as well. I think part of why it affects FAH has to do with the quick return bonus on FAH, so it amplifies what might be small changes in the actual time per fold, but I'm not sure on that. Good thread - I'll follow it to see what everybody else's experience is.
 

jebo_4jc

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Thanks for sharing your thoughts.

I've been thinking....with the way today's CPUs boost (high single thread performance, lower all core performance), it wouldn't take too much variance for the GPU PPD lost to outweigh the CPU PPD gain.
 

MN Scout

Supreme [H]ardness
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Try downclocking the 3600 frequency by X%, and see if the time to complete a work unit increases X%. Might be quick to test.
 

MN Scout

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Report back and let us know if your average WU times get better.
 

10esseeTony

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I don't expect you will see much change if any, staying within the Ryzen 3000 lineup, at least not on a 1080. That whole CPU lineup kicks some booty.

My experience comes from running 1070's on XEON v3 at 2.3MHz, vs 3.3MHz on a non XEON CPU of the same architecture, and the 1070 took a hit of about 70k ppd, with the slower processor, IIRC, under Windows.
 

jebo_4jc

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It might have been better to wait a week or so, the 5000 series ryzen's will be out with a major uplift in ipc
I know. I found a guy on Reddit who swapped my 3600 for the 3900X for a good deal. If I can get my hands on a 5900X I will buy it and sell the 3900X. I'm predicting availability on the Ryzen will suck as bad as everything else does right now though.
 
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