I noticed that by default, Qubes OS has voluntary kernel preemption as opposed to full preemption. I found that enabling full preemption (preempt=full on kernel command line) makes the system significantly more responsive under heavy I/O load. In particular, if I build a kernel in a Qubes OS VM, it significantly degrades responsiveness without preempt=full. With preempt=full, the system remains responsive. The storage stack used is LVM thin provisioning on LUKS, and I have observed significant CPU usage in dom0 kernel threads with names that indicate they are related to dm-thin and dm-crypt.
The kernel config used by the Qubes kernel package I use (6.1.28) is based on Fedora 37’s config, and Marek Marczykowski-Górecki (CCd) indicated that the same arguments apply to Fedora. Therefore, I am asking if Fedora should use full kernel preemption by default. -- Sincerely, Demi Marie Obenour (she/her/hers)
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