Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

[Alan Stern]

On Fri, 14 May 2010, Magnus Damm wrote:

> I agree with you Tony. I thought shutting down CPUs for power
> managment purposes could be done without freezing user space. At least
> that's what we do today with SH-Mobile.

If you can shut down and restart CPUs in the time periods between 
transitions into and out of the idle loop, then yes -- userspace 
doesn't need to be suspended.  After all, if the idle loop is running 
then no user threads are runnable.  (Not necessarily true on SMP 
systems, but you know what I mean.)

> Still not sure how the system wide suspend is different from Runtime
> PM and CPUidle from the hardware perspective...

For embedded systems, apparently the difference is minimal.  For other
systems, like ACPI-based PCs, there is a big difference: Powering down
devices and CPUs still leaves large parts of the system running.

In addition, these larger systems generally don't have aggressive 
runtime PM support, so a significant fraction (maybe more than 50%) of 
devices won't be powered down when they are idle -- whereas system 
suspend powers virtually everything down.

Alan Stern

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