[lkml]   [2007]   [Jul]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation
    On Thu, 12 Jul 2007, Jeremy Maitin-Shepard wrote:

    > "Rafael J. Wysocki" <> 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
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2007-07-13 05:21    [W:0.025 / U:3.776 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site