Re: [linux-pm] Re: Hibernation considerations

[david@lang.hm]

On Fri, 20 Jul 2007, Alan Stern wrote:

> On Fri, 20 Jul 2007 david@lang.hm wrote:
>
> > > Userspace can submit I/O requests.  Someone will have to audit every
> > > driver to make sure that such I/O requests don't cause a quiesced
> > > device to become active.  If the device is active, it will make the
> > > memory snapshot inconsistent with the on-device data.
> >
> > assuming this is the suspend-from-ram after a kexec back from the
> > write-to-disk kernel I don't think you are correct.
> >
> > when doing a suspend-to-ram you get to a point where you just don't use
> > any userspace.
>
> What do you mean?  How can you prevent user tasks from running?  That's
> basically what the freezer does, and the whole point of this approach
> is to eliminate the freezer.  Right?
>
> > from that point on you are just walking the device tree
> > putting things into low-power mode. This is the point where we are talking
> > about jumping to.
>
> Yes.  And putting things into low-power mode requires the ability to
> run the scheduler, which means that user tasks can be scheduled, which
> means that they can run.

I did not know that getting into low-power mode required scheduling.

does it require userspace?

if so this is a problem and I say punt on suspend-to-disk-and-ram until 
suspend-to-ram is working independantly ;-)

if not, then can you schedule but not consider non-kernel tasks runnable?

freezing all of userspace is easy (see above)

freezing all of kernelspace is easy (unplug all non-boot CPU's and don't 
schedule)

where freezing gets hard is when you need to partially freeze either one 
of these.

David Lang
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