Hi, On Wed, May 18, 2022 at 01:18:35PM +0530, Vivek Kumar wrote: > Kernel Hibernation > > Linux Kernel has been already supporting hibernation, a process which > involves freezing of all userspace tasks, followed by quiescing of all > kernel device drivers and then a DDR snapshot is taken which is saved > to disc-swap partition, after the save, the system can either shutdown > or continue further. Generally during the next power cycle when kernel > boots and after probing almost all of the drivers, in the late_init() > part, it checks if a hibernation image is present in the specified swap > slot, if a valid hibernation image is found, it superimposes the currently > executing Kernel with an older kernel from the snapshot, moving further, > it calls the restore of the drivers and unfreezes the userspace tasks. > CONFIG_HIBERNATION and a designated swap partition needs to be present > for to enable Hibernation. > > Bootloader Based Hibernation: > > Automotive usecases require better boot KPIs, Hence we are proposing a > bootloader based hibernation restore. At a high-level, I'm not a fan of adding new ways to enter the kernel, and for the same reasons that the existing hibernate handover is deliberately *not* a stable ABI, I don't think we should add an ABI for this. This is not going to remain maintainable or compatible over time as the kernel evolves. > Purpose of bootloader based hibernation is to improve the overall boot time > till the first display frame is seen on the screen or a camera application > can be launched from userspace after the power on reset key is pressed. Can you break down the time taken for that today? What does a cold boot look like? What *exactly* are you trying to skip by using hibernation? Thanks, Mark. > This RFC patchset > implements a slightly tweaked version of hibernation in which the > restoration of an older snapshot into DDR is being carried out from the > bootloader (ABL) itself, by doing this we are saving some time > (1 second measured on msm-4.14 Kernel) by not running a > temporary kernel and figuring out the hibernation image at late_init(). > In order to achieve the same bootloader checks for the hibernation > image at a very early stage from swap partition, it parses the image and > loads it in the DDR instead of loading boot image form boot partition. > Since we are not running the temporary kernel,which would have done some > basic ARM related setup like, MMU enablement, EL2 setup, CPU setup etc, > entry point into hibernation snapshot image directly from bootloader is > different, on similar lines, all device drivers are now re-programming > the IO-mapped registers as part of the restore callback (which is > triggered from the hibernation framework) to bring back the HW/SW sync. > > Other factors like, read-speed of the secondary storage device and > organization of the hibernation image in the swap partition effects the > total image restore time and the overall boot time. In our current > implementation we have serialized the allocation of swap-partition's slots > in kernel, so when hibernation image is being saved to disc, each page is > not scattered across various swap-slot offsets, rather it in a serial > manner. For example, if a DDR page at Page frame number 0x8005 is > located at a swap-slot offset 50, the next valid DDR page at PFN 0x8005 > will be preset at the swap-slot offset 51. With this optimization in > place, bootloader can utilize the max capacity of issuing a disc-read > for reading a bigger chunk (~50 MBs at once) from the swap slot, > and also parsing of the image becomes simpler as it is available > contiguously. > > > > Vivek Kumar (6): > arm64: hibernate: Introduce new entry point to kernel > PM: Hibernate: Add option to disable disk offset randomization > block: gendisk: Add a new genhd capability flag > mm: swap: Add randomization check for swapon/off calls > Hibernate: Add check for pte_valid in saveable page > irqchip/gic-v3: Re-init GIC hardware upon hibernation restore > > Documentation/admin-guide/kernel-parameters.txt | 11 ++ > arch/arm64/kernel/hibernate.c | 9 ++ > drivers/irqchip/irq-gic-v3.c | 138 ++++++++++++++++- > include/linux/blkdev.h | 1 + > kernel/power/snapshot.c | 43 ++++++++ > kernel/power/swap.c | 12 +++ > mm/swapfile.c | 6 +- > 7 files changed, 216 insertions(+), 4 deletions(-) > > -- > 2.7.4 >
