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

[Matthew Garrett <mjg59@srcf.ucam.org>]

On Thu, May 27, 2010 at 07:59:02PM +0200, Thomas Gleixner wrote:
> On Thu, 27 May 2010, Matthew Garrett wrote:
> > ACPI provides no guarantees about what level of hardware functionality 
> > remains during S3. You don't have any useful ability to determine which 
> > events will generate wakeups. And from a purely practical point of view, 
> > since the latency is in the range of seconds, you'll never have a low 
> > enough wakeup rate to hit it.
> 
> Right, it does not as of today. So we cannot use that on x86
> hardware. Fine. That does not prevent us to implement it for
> architectures which can do it. And if x86 comes to the point where it
> can handle it as well we're going to use it. Where is the problem ? If
> x86 cannot guarantee the wakeup sources it's not going to be used for
> such devices. The kernel just does not provide the service for it, so
> what ?

We were talking about PCs. Suspend-as-c-state is already implemented for 
OMAP.

> So the only thing you are imposing to app writers is to use an
> interface which solves nothing and does not save you any power at
> all. 

It's already been demonstrated that the Android approach saves power.

> Runnable tasks and QoS guarantees are the indicators whether you can
> go to opportunistic suspend or not. Everything else is just window
> dressing.

As I keep saying, this is all much less interesting if you don't care 
about handling suboptimal applications. If you do care about them then 
the Android approach works. Nobody has demonstrated a scheduler-based 
one that does.

-- 
Matthew Garrett | mjg59@srcf.ucam.org