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

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Message-ID: <Pine.LNX.4.44L0.0912171444040.2645-100000@iolanthe.rowland.org>
Date:	Thu, 17 Dec 2009 15:06:06 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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 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)

then we would reap close to the maximum benefit -- providing:

	async threads are started in a first pass without waiting
	for synchronous devices, and

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

Alan Stern

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