On Wed, Jul 10, 2019 at 11:28 AM Matthias Brugger <matthias.bgg@xxxxxxxxx> wrote: > > > > On 09/07/2019 20:20, Pavel Tatashin wrote: > > Changelog > > v1 - v2 > > - No changes to patches, addressed suggestion from James Morse > > to add "arm64" tag to cover letter. > > - Improved cover letter information based on discussion. > > > > Currently, it is only allowed to reserve memory for crash kernel, because > > it is a requirement in order to be able to boot into crash kernel without > > touching memory of crashed kernel is to have memory reserved. > > > > The second benefit for having memory reserved for kexec kernel is > > that it does not require a relocation after segments are loaded into > > memory. > > > > If kexec functionality is used for a fast system update, with a minimal > > downtime, the relocation of kernel + initramfs might take a significant > > portion of reboot. > > > > In fact, on the machine that we are using, that has ARM64 processor > > it takes 0.35s to relocate during kexec, thus taking 52% of kernel reboot > > time: > > > > kernel shutdown 0.03s > > relocation 0.35s > > kernel startup 0.29s > > > > Image: 13M and initramfs is 24M. If initramfs increases, the relocation > > time increases proportionally. > > > > While, it is possible to add 'kexeckernel=' parameters support to other > > architectures by modifying reserve_crashkernel(), in this series this is > > done for arm64 only. > > > > I wonder if we couldn't use the crashkernel reserved memory area for that and > just add logic to kexec-tools to pass to the kernel a flag (a new magic reboot > number?) to use the crashkernel memory for that? > The kernel would then unload the crash/capture system in the reserved memory > area and reuse the latter for kexec. > This would also enable the feature for all architectures. I decided to take another route: enable MMU during kernel relocation on ARM64. This will eliminate the problem that I am experiencing with slow relocation. Pasha > > Regards, > Matthias > > > The reason it is so slow on arm64 to relocate kernel is because the code > > that does relocation does this with MMU disabled, and thus D-Cache and > > I-Cache must also be disabled. > > > > Alternative solution is more complicated: Setup a temporary page table > > for relocation_routine and also for code from cpu_soft_restart. Perform > > relocation with MMU enabled, do cpu_soft_restart where MMU and caching > > are disabled, jump to purgatory. A similar approach was suggested for > > purgatory and was rejected due to making purgatory too complicated. > > On, the other hand hibernate does something similar already, but there > > MMU never needs to be disabled, and also by the time machine_kexec() > > is called, allocator is not available, as we can't fail to do reboot, > > so page table must be pre-allocated during kernel load time. > > > > Note: the above time is relocation time only. Purgatory usually also > > computes checksum, but that is skipped, because --no-check is used when > > kernel image is loaded via kexec. > > > > Pavel Tatashin (5): > > kexec: quiet down kexec reboot > > kexec: add resource for normal kexec region > > kexec: export common crashkernel/kexeckernel parser > > kexec: use reserved memory for normal kexec reboot > > arm64, kexec: reserve kexeckernel region > > > > .../admin-guide/kernel-parameters.txt | 7 ++ > > arch/arm64/kernel/setup.c | 5 ++ > > arch/arm64/mm/init.c | 83 ++++++++++++------- > > include/linux/crash_core.h | 6 ++ > > include/linux/ioport.h | 1 + > > include/linux/kexec.h | 6 +- > > kernel/crash_core.c | 27 +++--- > > kernel/kexec_core.c | 50 +++++++---- > > 8 files changed, 127 insertions(+), 58 deletions(-) > > _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
