On Fri, 20 Jul 2007, Alan Stern wrote:
On Fri, 20 Jul 2007 david@xxxxxxx 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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