It is a system wide configuration, yes, and what is disallowed by default is *reducing* niceness (ie: increasing priority, and that, to *any* level). It is IMO a stupid restriction, especially since it prevents a thread from getting back to its default niceness once it has increased it (which is always allowed). This is the reason for the `rlimit` check that is included here, used to determine the usable operating niceness range, so that we don't get stuck in a nice level we can't get out of. We also explicitly request the hard limit, so that the system can be configured with the existing default as a soft limit, as some sort of safety net against broken software. I think we should have support for it nonetheless, because it's the only reliable way to implement thread priorities (rtkit is a dead-end), and they have been reported to make a difference, greatly reducing stuttering when shaders are being compiled for instance. -- https://gitlab.winehq.org/wine/wine/-/merge_requests/4551#note_54435