GPU usage limiting?

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GPU usage limiting?

Postby Jack Brabham » Mon Feb 10, 2014 3:57 pm

Is there any way in the current software to limit GPU usage?
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Re: GPU usage limiting?

Postby PantherX » Mon Feb 10, 2014 4:39 pm

Welcome to the F@H Forum Jack Brabham,

Unfortunately, there isn't any way to limit the GPU Usage similar to limiting the CPU Usage. The reason is that the current GPUs don't have any kind of scheduling system unlike the CPU which has an advanced scheduling system managed by the operating system. This could theoretically change in the future with software advancements but for now, you can either fold on the GPU (either while you are using it or when the system is idle) or not.
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Re: GPU usage limiting?

Postby JimboPalmer » Mon Feb 10, 2014 5:18 pm

The 7.4.2 software has 'on idle' which only folds the GPU once the FAH screen saver has come on, if that helps.
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Re: GPU usage limiting?

Postby codysluder » Mon Feb 10, 2014 5:42 pm

JimboPalmer wrote:The 7.4.2 software has 'on idle' which only folds the GPU once the FAH screen saver has come on, if that helps.


So does V7.3 although there have been some issues associated with detecting an idle state depending on which OS you run.
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Re: GPU usage limiting?

Postby PantherX » Mon Feb 10, 2014 6:03 pm

For information on how the software detects the idle state, please read this which explains the idle detection for the supported operating systems (http://folding.stanford.edu/home/faq/fa ... ion/#ntoc3).
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Re: GPU usage limiting?

Postby Jack Brabham » Mon Feb 10, 2014 8:19 pm

Unfortunately the CPU usage also seems to all or nothing, changing the CPU usage bar has no effect.so I uninstalled the software. If I can't control it, I can't use it.

If it gets fixed someday I'll reconsider.

Thanks,

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Re: GPU usage limiting?

Postby P5-133XL » Tue Feb 11, 2014 2:17 am

The CPU usage bar is for uniprocessor cores which effectively do not exist anymore because even uniprocessor is being done by an SMP core now. If you want to limit the CPU you can manually choose how many CPU threads (in the Slots tab) and that will specify the number of CPU Cores to use. With a Quad core you have a granularity of 25% and an eight core (Including HT) you will have a granularity of 12.5%.
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Re: GPU usage limiting?

Postby Jack Brabham » Tue Feb 11, 2014 2:35 am

I've been away from folding@home (I am team 196148) for a while but I'm sure I remember being able to limit GPU usage in the past. This is a heat management issue as well as basically wanting to be able to use the PC while folding. Is it possible to go back to an older version that allows GPU usage management?
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Re: GPU usage limiting?

Postby P5-133XL » Tue Feb 11, 2014 2:41 am

There was a old v7 client that tried GPU limiting but it didn't work as expected or very well at all so it was removed. What it did was run the GPU at 100% for an interval of time and then 0% for an interval of time. The problem was it could not get the intervals fast enough to be useful so that all it did was effectively power/heat-cycle the GPU and lots of hot/cold power cycles is actually harmful.
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Re: GPU usage limiting?

Postby PantherX » Tue Feb 11, 2014 7:40 pm

The current FahCore_17 has a feature that allows you to stop GPU folding when it reaches a specific temperature (https://folding.stanford.edu/home/chang ... -full-fah/). However, it is disabled by default and can run only on single Nvidia GPU systems.
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Re: GPU usage limiting?

Postby bruce » Tue Feb 11, 2014 9:42 pm

As has already been said, the GPU has no concept of priority or time-slices or any of the other features that have been used to limit CPU usage. Even with all those features, modulating the CPU usage doesn't work very well except by limiting the number of CPU tasks that can be assigned to less CPUs than you have.

Now consider your GPU. Assign it a block of work that it can complete in X µs. It works as hard as possible to complete that block of work. By refusing to give it more work for X+Y µs, you might be able to limit the average throughput but as P5-133XL suggests, you'll be averaging busy time with idle time. Now consider somebody who has a faster or slower GPU. Any values chosen for X or Y will have different results because the two GPUs can process the GFLOPS in that work packet at a different rate. Then, too, the GPU also accepting work from other sources (such as a screen refresh or video decode or whatever) which tend to fill in the idle times, if there are any, with productive work so the average can drift.

In effect, you can turn off the GPU thermally or you can turn it off until the system is stable, by actually modulating the processing is essentially impossible. Repeated on and off cycles at a rate of 1/(X+Y) isn't good for your GPU.
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