linux-kernel - Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

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Date:	Thu, 17 Dec 2009 21:36:36 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

On Thursday 17 December 2009, Alan Stern wrote:
> On Thu, 17 Dec 2009, Rafael J. Wysocki wrote:
> 
> > That actually is correct.  On the nx6325 suspend is totally dominated by disk
> > spindown, almost everything else is negligible compared to it (well, except for
> > the audio), so we can't go down below 1 s during suspend on this box.
> > 
> > On the Wind, disk spindown time is comparable with serio suspend time,
> > so at least in principle we should be able to get .5 s suspend on this box - 
> > if the disk spindown in async.
> > 
> > In turn, the resume on the Wind is dominated by disk spinup, so we can't
> > go below 1.5 s on this box during resume (notice that the "async+extra"
> > approach brings us close to this limit, although we could save .5 s more in
> > principle by making more devices async).
> > 
> > Resume on the nx6325 is a different story, though, as it is dominated by USB
> > and PCI devices, so marking those as async would probably bring us close to
> > the limit.
> 
> The implications seem pretty clear.  If the following sorts of devices
> were async:
> 
> 	USB (devices and interfaces), PCI, serio, SCSI (hosts, targets,
> 	devices)

Plus ACPI battery.

> then we would reap close to the maximum benefit -- providing:
> 
> 	async threads are started in a first pass without waiting
> 	for synchronous devices, and

Agreed.
 
> It's not clear that making all these types of devices async will really 
> work, but it's worth testing.

I'm working on it.

Rafael
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