The true value of threads parameter when solving a problem

Answered

Chongyue Xu

September 20, 2023 15:34

My computer has 6 physical cores and 12 logical processors. When I set the Threads parameter to 20, Gurobi prints:

Thread count (20) is larger than processor count (12)
Reduce the value of the Threads parameter to improve performance.

And I'm wondering the true value of the Threads parameter when gurobi tries to solve the problem.

Thanks!

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3 comments

Simranjit Kaur
Gurobi Staff

September 20, 2023 22:35
As mentioned in our documentation, Gurobi will try to use as many threads as there are logical processors when the Threads parameter is left at its default value.

The maximum number of threads used during an optimization run is printed in the log, for example,
```
Thread count: 8 physical cores, 16 logical processors, using up to 16 threads
```
1
Chongyue Xu

September 21, 2023 10:40
Hi Simranjit:

Thanks for your answer. But actually I wanna know the number of threads used when I set the value of this parameter larger than the PC has. For example, thread count is 8 physical cores, 16 logical processors and I set the threads parameter to 20. Then what's the real threads used during the optimization? Looking forward to your reply, thanks.
```
8 physical cores, 16 logical processors
```
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Simranjit Kaur
Gurobi Staff

September 22, 2023 03:18
Hi Chongyue,

If you set the threads parameter to 20, Gurobi will try to use up to 20 threads.
```
Thread count: 8 physical cores, 16 logical processors, using up to 20 threads

Warning: Thread count (20) is larger than processor count (16)
         Reduce the value of the Threads parameter to improve performance
```
Please note if you request Gurobi to use a greater number of threads than the available CPU cores, the operating system will need to manage the distribution of these threads, often resulting in decreased performance.

Best regards,
Simran
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