Ok, I now reserved in the GRUB isolcpus=0-3. And then run with taskset --cpu-list 0-3.
However, I checked and all my three threads (see TRentrantRWlock thread lock, program freezes - #6 by ferhue) are running on the same CPU, namely number 0.
Is there a way to set the cpu affinity in a TThread class, in a similar way as done with std::thread https://stackoverflow.com/a/57620568/7471760? → I created a PR Allow specifying pthread CPU affinity by ferdymercury · Pull Request #8557 · root-project/root · GitHub