Enable MMU during kexec relocation in order to improve reboot performance. If kexec functionality is used for a fast system update, with a minimal downtime, the relocation of kernel + initramfs takes a significant portion of reboot. The reason for slow relocation is because it is done without MMU, and thus not benefiting from D-Cache. Performance data ---------------- For this experiment, the size of kernel plus initramfs is small, only 25M. If initramfs was larger, than the improvements would be greater, as time spent in relocation is proportional to the size of relocation. Previously: kernel shutdown 0.022131328s relocation 0.440510736s kernel startup 0.294706768s Relocation was taking: 58.2% of reboot time Now: kernel shutdown 0.032066576s relocation 0.022158152s kernel startup 0.296055880s Now: Relocation takes 6.3% of reboot time Total reboot is x2.16 times faster. Previous approaches and discussions ----------------------------------- https://lore.kernel.org/lkml/20190709182014.16052-1-pasha.tatashin@xxxxxxxxxx reserve space for kexec to avoid relocation, involves changes to generic code to optimize a problem that exists on arm64 only: https://lore.kernel.org/lkml/20190716165641.6990-1-pasha.tatashin@xxxxxxxxxx The first attempt to enable MMU, some bugs that prevented performance improvement. The page tables unnecessary configured idmap for the whole physical space. https://lore.kernel.org/lkml/20190731153857.4045-1-pasha.tatashin@xxxxxxxxxx No linear copy, bug with EL2 reboots. Pavel Tatashin (8): kexec: quiet down kexec reboot arm64, mm: transitional tables arm64: hibernate: switch to transtional page tables. kexec: add machine_kexec_post_load() arm64, kexec: move relocation function setup and clean up arm64, kexec: add expandable argument to relocation function arm64, kexec: configure transitional page table for kexec arm64, kexec: enable MMU during kexec relocation arch/arm64/Kconfig | 4 + arch/arm64/include/asm/kexec.h | 51 ++++- arch/arm64/include/asm/pgtable-hwdef.h | 1 + arch/arm64/include/asm/trans_table.h | 68 ++++++ arch/arm64/kernel/asm-offsets.c | 14 ++ arch/arm64/kernel/cpu-reset.S | 4 +- arch/arm64/kernel/cpu-reset.h | 8 +- arch/arm64/kernel/hibernate.c | 261 ++++++----------------- arch/arm64/kernel/machine_kexec.c | 199 ++++++++++++++---- arch/arm64/kernel/relocate_kernel.S | 196 +++++++++--------- arch/arm64/mm/Makefile | 1 + arch/arm64/mm/trans_table.c | 273 +++++++++++++++++++++++++ kernel/kexec.c | 4 + kernel/kexec_core.c | 8 +- kernel/kexec_file.c | 4 + kernel/kexec_internal.h | 2 + 16 files changed, 758 insertions(+), 340 deletions(-) create mode 100644 arch/arm64/include/asm/trans_table.h create mode 100644 arch/arm64/mm/trans_table.c -- 2.22.0
