1. Please describe the problem: PREEMPT_RT was fully merged and enabled in mainline Linux on the supported architectures x86, x86_64, RISC-V and ARM64. On the kernel 6.13 rc0 in Rawhide, we can't enable rt on the fly because PREEMPT_RT not set in the kernel. Can you enable this option ? For Rawhide, and FC40 and FC41 for the future kernel 6.12 stable ? (to test for testdays next week) 2. What is the Version-Release number of the kernel: 6.13.0-0.rc0.20241125git9f16d5e6f220.8.fc42.x86_64 3. Did it work previously in Fedora? If so, what kernel version did the issue *first* appear? Old kernels are available for download at https://koji.fedoraproject.org/koji/packageinfo?packageID=8 : New functionality 4. Can you reproduce this issue? If so, please provide the steps to reproduce the issue below: On kernel 6.13 in rawhide, at GRUB, add options : preempt=rt threadirqs Boot the system uname -a displays PREEMPT_DYNAMIC instead of PREEMPT_RT cat /sys/kernel/realtime : no such file or directory 5. Does this problem occur with the latest Rawhide kernel? To install the Rawhide kernel, run ``sudo dnf install fedora-repos-rawhide`` followed by ``sudo dnf update --enablerepo=rawhide kernel``: Yes 6. Are you running any modules that not shipped with directly Fedora's kernel?: No 7. Please attach the kernel logs. You can get the complete kernel log for a boot with ``journalctl --no-hostname -k > dmesg.txt``. If the issue occurred on a previous boot, use the journalctl ``-b`` flag. cat /proc/cmdline : BOOT_IMAGE=(hd0,gpt2)/vmlinuz-6.13.0-0.rc0.20241125git9f16d5e6f220.8.fc42.x86_64 root=/dev/mapper/fedora-root ro resume=/dev/mapper/fedora-swap rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap rhgb quiet rd.driver.blacklist=nouveau modprobe.blacklist=nouveau selinux=0 preempt=rt theadirqs uname -a : Linux fedorarhpx 6.13.0-0.rc0.20241125git9f16d5e6f220.8.fc42.x86_64 #1 SMP PREEMPT_DYNAMIC Mon Nov 25 18:47:15 UTC 2024 x86_64 GNU/Linux dmesg : nov. 28 21:52:19 kernel: Dynamic Preempt: unsupported mode: rt Full dmesg in the bug Reproducible: Always
Created attachment 2060231 [details] journalctl --no-hostname -k > dmesg.txt
You misunderstand what PREEMPT_RT is. It is not just a preemption mode, and it can not be enabled dynamically through PREEMPT_DYNAMIC and a kernel cmdline. It requires a separate kernel build and has specific use cases. We are in the process of getting sources ready so that you can build an RT fedora kernel from kernel-ark or from the srpm, but we have not yet decided whether or not we will ship one. Currently, there are some missing latency fixes for i915 and a couple of other drivers which make 6.12 a less than ideal candidate if we do decide to ship one.