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

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Date:	Tue, 15 Dec 2009 10:55:52 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>, 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 Tue, 15 Dec 2009, Linus Torvalds wrote:

> My whole point was that by doing the whole "wait for children" in generic 
> code, you also made devices - such as PCI bridges - have to wait for 
> children, even though they don't need to, and don't want to.
> 
> So I suggested an admittedly ugly hack to take care of it - rather than 
> some complex infrastructure.

It doesn't feel like an ugly hack to me.  It seems like exactly the 
Right Thing To Do: Make as many devices as possible use async 
suspend/resume.

The only reason we don't make every device async is because we don't
know whether it's safe.  In the case of PCI bridges we _do_ know --
because they don't have any work to do outside of
late_suspend/early_resume -- and so they _should_ be async.

The same goes for devices that don't have suspend or resume methods.

There remains a separate question: Should async devices also be forced
to wait for their children?  I don't see why not.  For PCI bridges it
won't make any significant difference.  As long as the async code
doesn't have to do anything, who cares when it runs?

Alan Stern

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