Messages in this thread | | | Date | Thu, 12 Jul 2007 20:12:33 -0700 (PDT) | From | david@lang ... | Subject | Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation |
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On Thu, 12 Jul 2007, Jeremy Maitin-Shepard wrote:
> "Rafael J. Wysocki" <rjw@sisk.pl> writes: > > [snip] > >> There's more to it, though. If devices are suspended, the hibernation kernel >> will have to resume them (using platform, like ACPI, callbacks in the process) >> instead and that will get complicated. > >> It's better if devices are quiesced, or even shut down, before we call the >> hibernation kernel. > > I agree that they definitely should not be put into a low power mode, as > that has nothing to do with hibernation. > > Ideally, the following would be done: > > All of the hardware that won't be needed by the "save image" kernel will > be shut down. The normal driver shut down calls may not be suitable, > however, because although the same thing should be done to the hardware, > the device shouldn't be "unregistered", since unlike in the actual > shutdown case, the same device will need to brought back up again on > resume, and it will need to have the same device id and such (and > userspace probably shouldn't see the device going away). > > Any devices that will be needed by the "save image" kernel could also > safely be shutdown as with the unneeded devices, but it would be more > efficient to simply quiesce it. Since this would be an additional > complication, initially probably all of the hardware should be shut > down, rather than quiesced. > > The reason that I think it is useful to actually shut down the devices, > rather than merely leaving some unneeded devices quiesced, is that it > would be useful to be able to build the "save image" kernel without > support for unneeded devices. In order to support "suspend to ram" > instead of shutting down after saving the image to disk, the hibernate > kernel needs to be able to send devices into a low power state. My > impression is that if there are devices it does not know about (i.e. the > unneeded devices), but which are left quiesced but powered on, this > would be a problem for suspend to ram, although not knowing much about > how suspend to ram actually works, I could be mistaken. (Maybe it is > possible through ACPI or standard bus interfaces to shut down all of the > devices without really knowing anything about them.)
I don't think that anyone is talking about useing kexec for suspend-to-ram, only for suspend-to-disk (hibernate)
>>>>> 3. Support the in-place kexec? The relocatable kernel is not necessary >>>>> if this can be implemented. >>>>> 4. Image writing/reading. (Only user space application is needed). >>>> >>>> And a kernel interface for that application. >>> >>> I do't understand this statement, this application is just useing the >>> standard kernel interfaces (block devices to read/write to disk, network >>> devices to read/write to a server, etc). no new interfaces needed. > >> Yes, but it will have to know _what_ to save, no? > > I agree that a kernel interface would be important; something like > /dev/snapshot that can be read by the "save image" kernel, and written > to by the "restore image" kernel. Note that similarly, kdump provides a > kernel interface to an ELF image of the old kernel.
I thought that the idea was to save the entire contents of ram so that caches, etc remain populated.
having the system kernel free up ram and then making a sg list of what memory needs to be backed up would be a nice enhancement, but let's let that remain a future enhancement until everyone agrees that the basic approach works.
David Lang - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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