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

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Date:	Tue, 25 May 2010 01:38:16 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kevin Hilman <khilman@...prootsystems.com>
Cc:	felipe.balbi@...ia.com,
	Arve Hjønnevåg <arve@...roid.com>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	Paul Walmsley <paul@...an.com>
Subject: Re: [PATCH 0/8] Suspend block api (version 8)

On Tuesday 25 May 2010, Kevin Hilman wrote:
> "Rafael J. Wysocki" <rjw@...k.pl> writes:
> 
> > On Monday 24 May 2010, Felipe Balbi wrote:
> >> On Mon, May 24, 2010 at 02:46:54AM +0200, ext 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
> >> 
> >> funny thing is that even without sorting out the concerns plenty of 
> >> developers had on the other thread, this series is still taken. What's 
> >> the point in dicussing/reviewing the patches then ?
> >
> > I don't think the concerns you're referring to can be solved out.  
> > Some people just don't like the whole idea and I don't think there's
> > any way we can improve the patches to make them happy.  The only
> > "solution" they would be satisfied with would simply be rejecting
> > the feature altogether, although there are no practically viable
> > alternatives known to me.
> 
> I'm not sure who the "some people" you're referring to are, but I'll
> assume I'm included in that group.
> 
> I don't think this is a fair characterization of the objections, nor
> do I think "rejecting the feature altogether" is the only satisfactory
> answer.  Speaking for myself, I find the idea of being able to suspend
> while idle a valid objective, and certainly see the usefulness of it
> for embedded systems.  I'm also an owner and user of an Android phone,
> so I am certainly not out just to make life difficult for Android.
> 
> The primary objection is not the end goal, but rather the
> implementation.  In particular, the problematic redefintion of what it
> means to be idle, or "not doing work that's immediately useful to the
> user" to use the phrase from the changelog (where "useful" is still
> not defined.)

So, in fact, you don't like the _idea_, because the _idea_ is to use suspend
blockers instead of trying to define what "idle" means.

I don't think it's generally possible to define "idle" to match every possible
criteria one can imagine, so you're request to do that simply cannot be
satisfied.

> This (re)definition completely bypasses all current idle
> infrastructure based on timers, scheduler, etc. and makes "usefulness"
> defined in terms of who holds suspend blockers.

That's because the point is not to suspend when the system is "idle", because
that would mean "suspend transparently from the applications' point of view",
which is what the Android people _don't_ _want_ _to_ _do_, because in that
case their battery life would go to the toilet.  The idea is to suspend even
when the system is not techincally "idle" and you don't like _that_.

> This of course will lead to a scattering of suspend blockers into any
> drivers/subsystems considered "useful", which by looking through current
> Android kernels is many of them.

That depends on the maintainers of these subsystems, who still have the power
to reject requested changes.

As I said before, I don't think there's a way to resolve this so that everyone
is happy and in my opinion there are reasons to merge the feature.

Also I don't think we can make any progress discussing it.  We've already
discussed it for a month or so without any real progress and I don't see how
that's going to change now.

Thanks,
Rafael
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