On Thursday, 12 July 2007 08:43, david@xxxxxxx wrote: > On Wed, 11 Jul 2007, Jeremy Fitzhardinge wrote: > > > Andrew Morton wrote: > >> On Wed, 11 Jul 2007 15:30:31 +0000 > >> "Huang, Ying" <ying.huang@xxxxxxxxx> wrote: > >> > >> > 1. Boot a kernel A > >> > 2. Work under kernel A > >> > 3. Kexec another kernel B in kernel A > >> > 4. Work under kernel B > >> > 5. Jump from kernel B to kernel A > >> > 6. Continue work under kernel A > >> > > >> > This is the first step to implement kexec based hibernation. If the > >> > memory image of kernel A is written to or read from a permanent media > >> > in step 4, a preliminary version of kexec based hibernation can be > >> > implemented. > >> > > >> > The kernel B is run as a crashdump kernel in reserved memory > >> > region. This is the biggest constrains of the patch. It is planed to > >> > be eliminated in the next version. That is, instead of reserving memory > >> > region previously, the needed memory region is backuped before kexec > >> > and restored after jumping back. > >> > > >> > Another constrains of the patch is that the CONFIG_ACPI must be turned > >> > off to make kexec jump work. Because ACPI will put devices into low > >> > power state, the kexeced kernel can not be booted properly under > >> > it. This constrains can be eliminated by separating the suspend method > >> > and hibernation method of the devices as proposed earlier in the LKML. > >> > > >> > The kexec jump is implemented in the framework of software suspend. In > >> > fact, the kexec based hibernation can be seen as just implementing the > >> > image writing and reading method of software suspend with a kexeced > >> > Linux kernel. > >> > > > > > I guess I'm (still) confused by the terminology here. Do you mean that it > > fits into suspend-to-disk as a disk-writing mechanism, or in suspend-to-ram > > as a way of going to sleep? > > Suspend-to-ram involves stopping the system and shutting down devices to > go into low-power mode, then on wakeup restarting devices and resuming > operation > > so the steps would be. > > 1. stop userspace > > 2. walk the system device tree and put devices to sleep > > 3. go into the lowest power mode available and wait for a wakeup signal > > later > > 4. walk the system device tree and wake up devices > > 5. resume userspace scheduling. Note that we are going to phase out steps 1 and 5. > note that what devices get put to sleep could be configurable, potentially > to the extreme of things like the OLPC (that have hardware designed for > cheap sleeping) going into a light suspend-to-ram state between keystrokes > if nothing else has a timer event scheduled before that. > > Suspend-do-disk (Hibernate) involves stopping the system, makeing a > snapshot of ram, writing the snapshot to somewhere and powering off the > box. on wakeup (power-on) a helper kernel boots, loads the snapshot into > ram and jumps to the kernel in the snapshot to resume operation. > > as I understand the proposal the thought is to do the following > > 1. system kernel does suspend-to-ram to put the devices into a known safe > state. Not necessarily suspend-to-RAM. I'd much prefer it if devices were not put into low power states but quiesced (ie. no DMA, no interrupts). > 2. system kernel uses kexec to start hibernate kernel > > 3. hibernate kernel wakes up devices it needs as if it was doing a > resume-from-ram I think that the devices should be initialized from scratch in this step. > 4. hibernate kernel copies ram image somewhere In this step some userland may be involved (started from the "hibernate" kernel). > 5. hibernate kernel shuts down the box > > later > > 6. hibernate kernel boots > > 7. hibernate kernel copies ram image from somewhere > > 8. hibernate kernel does syspend-to-ram to put the devices into a known > safe state. Again, the devices should be quiesced rather then suspended in this step. > 9. hibernate kernel uses kexec to start system kernel > > 10. system kernel wakes up devices it needs as if it was doing a > resume-from-ram. I think it should reconfigure devices from scratch (ie. reprobe). > >> > Now, only the i386 architecture is supported. The patch is based on > >> > Linux kernel 2.6.22, and has been tested on my IBM T42. > >> > > >> > >> This sounds awesome. Am I correct in expecting that ultimately the > >> existing hibernation implementation just goes away and we reuse (and hence > >> strengthen) the existing kexec (and kdump?) infrastructure? > >> > >> And that we get hibernation support almost for free on all kexec (and > >> relocatable-kernel?) capable architectures? > >> > >> And that all the management of hibernation and resume happens in > >> userspace? > > this is the thought. > > >> I didn't understand the ACPI problem. Does this mean that CONFIG_ACPI > >> must > >> be disabled in the to-be-hibernated kernel, or in the little transient > >> kexec kernel? > >> > > > > I think the point is that if kernel A says "I'm suspending" and calls the > > suspend method on all its devices, then kernel B finds that it has no powered > > on devices to work with. But then couldn't it turn on the ones it wants > > anyway? And don't you want to suspend them, to make sure they're not still > > DMAing memory while B is trying to shuffle everything off to disk? > > I don't understand the ACPI problem so I can't try to clarify it. > > > It does sound pretty cool. > > re-useing existing components in new ways, making it so that particular > problems only have to be solved once and that solution is used repeatedly. > there's a lot to like about this approach. > > very cool. Well, I'm not a big fan of it right now, but well, it looks doable in general. Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
