Messages in this thread | | | Date | Fri, 20 Jul 2007 14:34:02 -0700 (PDT) | From | david@lang ... | Subject | Re: [linux-pm] Re: Hibernation considerations |
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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.
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