Hi, On 2023-10-08 07:17, Diederik de Haas wrote: > $ grep PREEMPT_DYNAMIC /boot/config-6.5.0-1-amd64 > CONFIG_PREEMPT_DYNAMIC=y > CONFIG_HAVE_PREEMPT_DYNAMIC=y > CONFIG_HAVE_PREEMPT_DYNAMIC_CALL=y
[...] > $ grep PREEMPT_DYNAMIC /boot/config-6.1.0-13-arm64 > # CONFIG_PREEMPT_DYNAMIC is not set > CONFIG_HAVE_PREEMPT_DYNAMIC=y > CONFIG_HAVE_PREEMPT_DYNAMIC_KEY=y CONFIG_PREEMPT_DYNAMIC is set to 'y' by default on amd64 due to HAVE_PREEMPT_DYNAMIC_CALL being 'y', see: https://sources.debian.org/src/linux/6.5.6-1/kernel/Kconfig.preempt/?hl=101#L101 arm64 does not have PREEMPT_DYNAMIC_CALL, this is why PREEMPT_DYNAMIC is not set by default there. However, there's another feature which is functionally equivalent, PREEMPT_DYNAMIC_KEY. While _CALL and _KEY are equivalent, in theory _KEY may have more overhead. See: https://lore.kernel.org/lkml/20220214165216.2231574-1-mark.rutl...@arm.com/#t SUSE and Fedora both seem to have CONFIG_HAVE_PREEMPT_DYNAMIC=y on arm64, see: https://github.com/SUSE/kernel-source/blob/SLE15-SP6/config/arm64/default#L123 https://src.fedoraproject.org/rpms/kernel/blob/f34/f/kernel.spec#_4458 Setting CONFIG_HAVE_PREEMPT_DYNAMIC=y on arm64 is likely safe for us too, but we may want to run some benchmark first to see if there are any noticeable slowdowns.
