Proton/docs/THREAD_PRIORITY.md

Thread priorities

Proton supports fine-grained thread priority control using setpriority(2) to set thread niceness values corresponding to the game threads' Windows base priority levels. However, most default Linux configurations don't allow individual threads to raise their priority, so some system configuration is likely required.

It can be configured as a privileged user by editing the /etc/security/limits.conf file, or using the /etc/security/limits.d/ conf directory, and adding the following line at the end:

*   hard  nice    -15

Where -15 could be any value between [-20,0] that will correspond to the minimum niceness (the highest priority) a thread can get to. The lower the value, the more CPU time a high priority thread will get, at the expense of others and other processes, possibly making the system less responsive.