I just upgraded from Gurobi 9.0.3 to 9.1.1 and noticed that MIPs were solving much slower than in the previous release. After inspecting CPU usage in Windows task manager during the solve I noticed that Gurobi was only using a single core during the MIP phase in 9.1.1. All cores are used in Barrier in LP problems or during the root relaxation phase of MIPs, but only a single core during branch-and-bound. I have the Threads parameter set to 12. When I downgrade to 9.0.3 again everything is fine - i.e. all cores are used during the MIP phase using the exact same code.
I get the same behavior on two different machines. Is this just me, a problem with Julia's Gurobi interface or a general Gurobi issue?
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