Depending on the size and complexity of the analysis you are solving, system performance can become an issue. The GeoStudio System Requirements article outlines some considerations for optimal performance. Read this first to see if there are any factors that may be affecting the specific type of analysis you are trying to solve.
Generally, the priority of the solving processes is lowered below the priority of the UI processes. This should allow the UI to remain responsive. If your responsiveness is still hampered by solving, there are some options available to you to limit the number of cores used for solving:
Basically, the environment variable OMP_NUM_THREADS will specify the initial number of threads assigned to a multi-threaded block of processing. GeoStudio will launch n simultaneous solves and within those solves, launch n threads. By raising or lowering the number assigned to OMP_NUM_THREADS, you can increase or decrease the number of threads assigned rather than have GeoStudio manage thread assignment.
For instance, setting OMP_NUM_THREADS to 3 means that for each solve, three threads are launched. So if 3 solves are launched in parallel, you would have a total of 9 threads being used.
Be aware that using the OMP_NUM_THREADS environment variable will affect all other applications running on the computer.
To set this environment variable: