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

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Message-Id: <200912201910.26895.rjw@sisk.pl>
Date:	Sun, 20 Dec 2009 19:10:26 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	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 Sunday 20 December 2009, Alan Stern wrote:
> On Sun, 20 Dec 2009, Rafael J. Wysocki wrote:
> 
> > > It's too early to come to this sort of conclusion (i.e., that suspend
> > > and resume react very differently to an asynchronous approach).  Unless
> > > you have some definite _reason_ for thinking that resume will benefit
> > > more than suspend, you shouldn't try to generalize so much from tests
> > > on only two systems.
> > 
> > In fact I have one reason.  Namely, the things that drivers do on suspend and
> > resume are evidently quite different and on these two systems I was able to
> > test they apparently took different amounts of time to complete.
> > 
> > The very fact that on both systems resume is substantially longer than suspend,
> > even if all devices are suspended and resumed synchronously, is quite
> > interesting.
> 
> Yes, it is.  But it doesn't mean that suspend won't benefit from 
> asynchronicity; it just means that the benefits might not be as large 
> as they are for resume.

Agreed, although that rises the question whether they are sufficiently
significant.  I guess time will tell.  With the i8042 done asynchronously they
are IMO.

BTW, what's the right place to call device_enable_async_suspend() for USB
devices?

Rafael
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