Re: [PATCH v1 0/8] arm64: MMU enabled kexec relocation

[Pavel Tatashin]

Just a friendly reminder, please send your comments on this series.
It's been a week since I sent out these patches, and no feedback yet.
Also, I'd appreciate if anyone could test this series on vhe hardware
with vhe kernel, it does not look like QEMU can emulate it yet

Thank you,
Pasha

On Thu, Aug 1, 2019 at 11:24 AM Pavel Tatashin
<pasha.tatashin@xxxxxxxxxx> wrote:
>
> 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
>