Hi Pavel, On 09/07/2019 11:55, Pavel Tatashin wrote: > On Tue, Jul 9, 2019 at 6:36 AM Bhupesh Sharma <bhsharma@xxxxxxxxxx> wrote: >> On Tue, Jul 9, 2019 at 2:46 AM Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> wrote: >>> 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. >> >> This seems like an issue with time spent while doing sha256 >> verification while in purgatory. >> >> Can you please try the following two patches which enable D-cache in >> purgatory before SHA verification and disable it before switching to >> kernel: >> >> http://lists.infradead.org/pipermail/kexec/2017-May/018839.html >> http://lists.infradead.org/pipermail/kexec/2017-May/018840.html > > Hi Bhupesh, > > The verification was taking 2.31s. This is why it is disabled via > kexec's '-i' flag. Therefore 0.35s is only the relocation part where > time is spent, and with my patches the time is completely gone. > Actually, I am glad you showed these patches to me because I might > pull them and enable verification for our needs. > >> >> Note that these were not accepted upstream but are included in several >> distros in some form or the other :) > > Enabling MMU and D-Cache for relocation would essentially require the > same changes in kernel. Could you please share exactly why these were > not accepted upstream into kexec-tools? Because '--no-checks' is a much simpler alternative. More of the discussion: https://lore.kernel.org/linux-arm-kernel/5599813d-f83c-d154-287a-c131c48292ca@xxxxxxx/ While you can make purgatory a fully-fledged operating system, it doesn't really need to do anything on arm64. Errata-workarounds alone are a reason not do start down this path. Thanks, James _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
