linux-kernel - Re: [GIT PULL] PM updates for 2.6.33

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Message-ID: <20091206213112.568c602b@infradead.org>
Date:	Sun, 6 Dec 2009 21:31:12 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [GIT PULL] PM updates for 2.6.33

On Sun, 6 Dec 2009 18:27:07 -0800
Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:

> On Sun, Dec 06, 2009 at 05:18:56PM -0800, Arjan van de Ven wrote:
> > On Sun, 6 Dec 2009 14:54:48 -0800
> > Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> > 
> > > Yes, that's your PS/2 mouse (rather touchpad) and the delay comes
> > > from device reset (needed by some keyboard controllers - I
> > > remember HP -or it and keyboard will be dead at resume).
> > > 
> > 
> > btw could we do this reset in an async function call (as long as we
> > wait for it to complete before we pull the plug finally) ?
> 
> It has to complete before we start shutting down i8042, so there are
> dependencies involved...

async function calls have 2 methods for synchronization:

* inside an async function, you can wait for all "earlier" async
  functions to complete  (async_synchronize_cookie)
* outside an async function, you can wait for all scheduled async
  functions to complete (async_synchronize_full)

so there's two options to use the async code to cut down this time:

1) Make both the mouse, keyboard AND the i8042 suspend functions async,
   and in the i8042 function the code first synchronizes on all previous
   async work
2) only make the mouse and keyboard suspend async, and just wait for all
   async work in i8042 suspend

I strongly prefer number 1, in terms of getting the best suspend speed.
It means that all other suspend code can run in parallel to the whole
serio/i8042 suspend.
Option two is simpler, but the delay is in the normal, synchronous path,
so other suspend code will not run in parallel.

The good news is that neither is hard for someone familiar with the
code...


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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