linux-kernel - Re: [PATCH 0/8] Suspend block api (version 8)

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Message-ID: <20100526114053.440c0559@schatten.dmk.lab>
Date:	Wed, 26 May 2010 11:40:53 +0200
From:	Florian Mickler <florian@...kler.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arve Hjønnevåg <arve@...roid.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] Suspend block api (version 8)

On Wed, 26 May 2010 10:45:33 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, 2010-05-24 at 02:46 +0200, Rafael J. Wysocki wrote:
> > On Saturday 22 May 2010, Arve Hjønnevåg wrote:
> > > This patch series adds a suspend-block api that provides the same
> > > functionality as the android wakelock api. This version adds a
> > > delay before suspending again if no suspend blockers were used
> > > during the last suspend attempt.
> > 
> > Patches [1-6/8] applied to suspend-2.6/linux-next
> 
> So you're going to merge this junk?
> 
> 

Yes. By now, everyone reading the posts should know all points.
Raffael obviously was part of this discussion and came to the decision
to merge it. 

My take of the discussion:
_IF_ you want to suspend aggressively, I don't see another
way.

The thing is, this is a paradigm change. Suspend is not anymore
controlled by userspace. In order to let userspace control/work with
this scheme, it needs to know when a suspend will be successfull or
poll:

1. kernel sees suspend may be possible on his side of things

2. kernel sends a message to userspace that i could be possibly
possible to suspend, but it may well be that by the time
userspace suspends it is not possible anymore

3. userspace decides to suspend. 

<- system suspends...  or not ..-> 

4. userspace retries ... retries ... retries ... 

And then you have the whole can of worms and races.

Or you have the suspend-blocker scheme:

1. kernel sees suspend is possible.
2. kernel suspends.
3. bingo.

Cheers,
Flo
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