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

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Date:	Sat, 19 Dec 2009 22:41:03 +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 Friday 18 December 2009, Alan Stern wrote:
> On Fri, 18 Dec 2009, Rafael J. Wysocki wrote:
> 
> > I didn't manage to do that, but I was able to mark sd and i8042 as async and
> > see the impact of this.
> 
> Apparently this didn't do what you wanted.  In the nx6325
> sd+i8042+async+extra log, the 0:0:0:0 device (which is a SCSI disk) was
> suspended by the main thread instead of an async thread.

Hm, that's odd, because there's a noticeable time difference between the
two cases in which the sd is sync and async.  I'll look into it further.

> There's an important point I neglected to mention before.  Your logs 
> don't show anything for devices with no suspend callbacks at all.  
> Nevertheless, these devices sit on the device list and prevent other
> devices from suspending or resuming as soon as they could.

Unless they are async, that is.

> For example, the fingerprint sensor (3-1) took the most time to resume.  
> But other devices were delayed until after it finished because it had
> children with no callbacks, and they delayed the devices following
> them in the list.
> 
> What would happen if you completed these devices immediately, as part 
> of the first pass?

OK.  How do the PM core is supposed to check if a device has null suspend
and resume?  Check all of the function pointers in the first pass?

Rafael
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