------- Comment From [email protected] 2026-06-05 11:37 EDT------- (In reply to comment #13) > The root cause of the problem is that s390x kernels are built with kernel > preemption enabled (CONFIG_PREEMPTION=y). On s390 that forces > CONFIG_GENERIC_LOCKBREAK=y. > > GENERIC_LOCKBREAK=y forces a generic, non-optimized, implementation of a > spinlock, instead of using the optimized arch_spin_lock_wait() (which is now > basically dead code). What actually runs therefore is a simple > compare-and-swap on a single shared word across all logical CPUs.
Yes, that makes a lot of sense. Thank you for your quick analysis! I just posted a corresponding patch for this: https://lore.kernel.org/linux-s390/[email protected]/T/#u -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2154748 Title: [Ubuntu 26.04] Severe Performance Degradation on kernel 7.0.0-15 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-z-systems/+bug/2154748/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
