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

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Message-Id: <200912201355.45760.rjw@sisk.pl>
Date:	Sun, 20 Dec 2009 13:55:45 +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 Sunday 20 December 2009, Alan Stern wrote:
> On Sat, 19 Dec 2009, Rafael J. Wysocki wrote:
> 
> > 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
> 
> To be precise, the device is an ATA or SATA disk but it is managed by 
> the sd driver.
> 
> > > 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.
> 
> I don't know what the whole story is, but the PID number tells the 
> tale.
> 
> > > 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.
> 
> Yes.  It would be simpler to make them async.  But first we ought to
> know what they are.  Can you add an extra line to the log for such
> devices?

Sure, I'll do that.

> What I'm afraid of is that there might be a "normal" device with a
> "normal" ancestor but with "abnormal" devices in between (where
> "normal" means there is a suspend or resume routine and "abnormal"  
> means all the method pointers are NULL).  I know that this happens when
> there's a USB mass-storage device, for example.  If we complete the
> intermediate devices immediately, then there won't be anything to
> prevent the ancestor from suspending before the device or the device
> from resuming before the ancestor.

I'm afraid of that too.

Rafael
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