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Processor usage cycles up and down?

Processor usage cycles up and down?

Questions and Answers : Windows : Processor usage cycles up and down?
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JMLVT68

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Message 50658 - Posted: 28 Oct 2014, 14:05:53 UTC

Running CP as the only BOINC project on Win 7 machine with i5 (Ivy Bridge) processor, which is 2 cores but 4 threads. So there are 4 tasks running simultaneously. I've noticed, watching Windows task manager, that the processor usage is cycling up and down, while keeping the average below the 50% max I've set on CPU usage. I also used Core Temp to check temperature, and noticed that the actual processor frequency was cycling, which seems odd. I did some testing, and found that if I increased the CPU limit to 90%, the cycling stopped.

Q1: Is there something in the way the models run that creates the cycling in processor usage?
Q2: Is the actual processor frequency cycling a function of trying to limit average usage to 50%?

My objective is to get good processing speed at moderate CPU load so I don't have to listen to the fan whining away keeping the system cool.

Thanks in advance
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Profile Iain Inglis
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Message 50659 - Posted: 28 Oct 2014, 14:40:10 UTC - in response to Message 50658.  

The BOINC CPU load management facility is pretty crude: it simply suspends the running applications to maintain the required load, which probably explains the cycling you can see.

It is also possible to limit the number of tasks being run (search for "cc_config.xml ncpus"). I have an old machine that blows its power supply if overloaded: to stop that happening again, the number of CPUs has been limited for that machine to one out of four. It crunches quite happily now - and quietly too.
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Les Bayliss
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Message 50661 - Posted: 28 Oct 2014, 19:07:58 UTC - in response to Message 50658.  

You could also implement the suggestions in my post here.

Using the 2 virtual cores doesn't add much to throughput, so setting the number of processors to 50% in your project preferences would be a better way to control heat.

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wateroakley

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Message 50699 - Posted: 31 Oct 2014, 13:36:48 UTC - in response to Message 50658.  
Last modified: 31 Oct 2014, 13:56:51 UTC

Q1: Is there something in the way the models run that creates the cycling in processor usage?
Q2: Is the actual processor frequency cycling a function of trying to limit average usage to 50%?

My objective is to get good processing speed at moderate CPU load so I don't have to listen to the fan whining away keeping the system cool.


A1. No. The cpu cycling is primarily a function of the cpu useage, not the current models. If you set BOINC to 100% cpu, the cpu cores will run at 100% almost all of the time, although you may see some dips for a very short time.

A2. Yes and no. If the BOINC cpu setting is 50%, the cpu frequency cycling up/down that you see in Core Temp is due to the i5 cpu internal features functioning as as Mr Intel designed them. The cpu features are also adjusted by the (default) power option settings in Win 7 managing the cpu. This is normal, as is the non-cycling frequency result at 90%, for the default power settings in Win 7. Speed-wise the turbo-boost can raise the default i5-3437U 1.9GHz speed to 2.9GHz.

The advanced Win 7 power settings include processor power management, with max/min % processor cpu, and the processor cooling policy.

The TDP heat dissipation of an i5-3437 is only 17W, the lowest of the low for a third generation cpu. Where cpu temperatures rise in extremis (eg due to a clogged fan) Mr Intel will reduce the i5-3437U cpu voltage VID and frequency to keep the cpu junction temperature Tj below the maximum design limit of 105 deg C. If the CPU temperature is too high for Mr Intel, Core temp will show a high temperature profile, with the frequency and VID changing, both rattling around.

If the cpu frequency is rattling around due to low cpu % utilisation, then the cpu heat dissipation will be below TDP, and the fan profile should set the fan revs at a lower (and quieter) speed. At high cpu load the VID and frequency buffers should kick in only after there is a noticeable increase in fan noise/speed.

You could test the fan noise level by running BOINC at 100% and, subject to the power settings, the cpu should run at maximum performance. If the noise is indeed intrusive, you can then then throttle back to an acceptable noise level and processing performance. As Les recommends I'd avoid limiting cpu by BOINC %, I'd limit the number of models by cpu/thread integers. That way Mr Intel manages the whole thing at the cpu level, and unintended issues from swapping models in/out is avoided.

Good luck.

Edits, minor clarifications.
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Questions and Answers : Windows : Processor usage cycles up and down?

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