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Hi we bought a nice computer to use to solve optimization problems.

Intel i7-980X@3,33 GHz with 12 GB of Team Group 1600 MHz DDR3 RAM.

When we use Gurobi the computer uses all 12 cores at maximum in the beginning of the solve. However after a while (about 8 hrs) it all cores jump between 65 and 85%

When I solve the same models on an i7 930 all cores are at a near 100% level even after longer solution times.

We first thought that the Hard disk was the bottleneck since Gurobi writes out nodefiles after the memorylimit is used.

However since the new computer have 12 GB of RAM we put the memorylimit to 7 GB so the solver only used the RAM and still with the same performance in the processor.

Any ideas about the bottleneck?

As I said earlier it works at 100% for the first hours or so . Thanks very much for any answers! Our plan was to overclock it but we can't even get it to work at normal speed yet!

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2 Answers 2

up vote 10 down vote accepted

My guess would be that it is throttling down due to heat issues.

Find an app that can report CPU temperature and see if the temperature rise correlates to a drop in CPU throughput.

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5  
This is exactly what I'd have thought. The i-series CPUs work within thermal and power limitations, and if it cannot shed heat fast enough (i.e. your cooling is rubbish) then it will throttle back until the CPU is not likely to kill itself with heat. Coretemp (alcpu.com/CoreTemp) can be useful to see the temperatures reported by the CPU, temperatures over 70 isn't great, over 80 is bad, and over 90 would be worrying... –  Mokubai Dec 31 '10 at 13:18
    
+1 answer due to heat –  therobyouknow Dec 31 '10 at 15:03
    
this seems reasonable! Will run some tests and come with some follow up questions if needed! Thanks very much! –  Buxley Jan 3 '11 at 6:55

Just to supplement @geoffc 's answer:

http://www.techpowerup.com/realtemp/ (Realtime GT) allows you to see separately the core temperatures of the i7-980X CPU.

To troubleshoot temperature problems:

  • Optimize airflow. Is there enough intake fans and outflow fans? Intake fans are more important than outflow fans because most cooling mechanisms in a PC is designed for positive pressure chassis. ( see http://www.silverstonetek.com.tw/tech/wh_positive.php )
  • Change the CPU cooler. There are many aftermarket coolers that can take much more heat than the stock intel cooler although I don't think a properly ventilated chassis would have problem with non-overclocked i7-980X CPU on stock cooler. Check tomshardware/anandtech for cooler comparisons. (Or hardocp, hexus, etc.) Consider reseating the CPU cooler after cleaning if you think it may not be properly placed. Note that you will need heatsink compound for this job.
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