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Date: Thu, 27 May 2010 18:30:41 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Matthew Garrett <mjg59@srcf.ucam.org>
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Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)
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> > Opportunistic suspend is just a deep idle state, nothing else.
> 
> No. The useful property of opportunistic suspend is that nothing gets 
> scheduled. That's fundamentally different to a deep idle state.

Nothing gets scheduled in a deep idle state either - its idle. We leave
the idle state to schedule anything.

I believe the constraint is

- Do not auto-enter a state for which you cannot maintain the devices in
  use "properly".

On a current PC that generally means 'not suspend', on a lot of embedded
boards (including Android phones) it includes an opportunistic 'suspend'
and also several states half way between the PC deepest idles and suspend.

> > Stop thinking about suspend as a special mechanism. It's not - except
> > for s2disk, which is an entirely different beast.
> 
> On PCs, suspend has more in common with s2disk than it does C states.

Todays PCs are a special case. More to the point I don't think anyone is
expected opportunistic suspend to be useful on _todays_ x86 systems.

Even on todays PCs your assumption is questionable for virtual machines
where a VM suspend is a lot faster and rather useful.

Alan