linux-kernel - Re: [linux-pm] suspend blockers & Android integration

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Date:	Thu, 10 Jun 2010 08:04:25 +1000
From:	Neil Brown <neilb@...e.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Felipe Contreras <felipe.contreras@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>, david@...g.hm,
	Florian Mickler <florian@...kler.org>,
	Vitaly Wool <vitalywool@...il.com>,
	Brian Swetland <swetland@...gle.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Arjan van de Ven <arjan@...radead.org>, tytso@....edu,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Felipe Balbi <felipe.balbi@...ia.com>
Subject: Re: [linux-pm] suspend blockers & Android integration

On Wed, 9 Jun 2010 11:40:27 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Wednesday 09 June 2010, Felipe Contreras wrote:
> > On Wed, Jun 9, 2010 at 6:46 AM, Linus Torvalds
> > <torvalds@...ux-foundation.org> wrote:
> > > On Tue, 8 Jun 2010, david@...g.hm wrote:
> > >>
> > >> having suspend blockers inside the kernel adds significant complexity, it's
> > >> worth it only if the complexity buys you enough. In this case the question is
> > >> if the suspend blockers would extend the sleep time enough more to matter. As
> > >> per my other e-mail, this is an area with rapidly diminishing returns as the
> > >> sleep times get longer.
> > >
> > > Well, the counter-argument that nobody seems to have brought up is that
> > > suspend blockers exist, are real code, and end up being shipped in a lot
> > > of machines.
> > >
> > > That's a _big_ argument in favour of them. Certainly much bigger than
> > > arguing against them based on some complexity-arguments for an alternative
> > > that hasn't seen any testing at all.
> > >
> > > IOW, I would seriously hope that this discussion was more about real code
> > > that _exists_ and does what people need. It seems to have degenerated into
> > > something else.
> > >
> > > Because in the end, "code talks, bullshit walks". People can complain and
> > > suggest alternatives all they want, but you can't just argue. At some
> > > point you need to show the code that actually solves the problem.
> > 
> > That's assuming there is an actual problem, which according to all the
> > embedded people except android, there is not.
> 
> Yes, there is, but they've decided to ignore it.
> 
> > And if there is indeed such a problem (probably not big), it might be
> > solved properly by the time suspend blockers are merged, or few
> > releases after.
> 
> Not quite.  Have you followed all of the discussion, actually?
> 
> > Whatever the solution (or workaround) is, it would be nice if it could
> > be used by more than just android people, and it would also be nice to
> > do it without introducing user-space API that *nobody* likes and might
> > be quickly deprecated.
> 
> I agree with Linus and I don't have that much of a problem with the API that
> people seem to have.  In fact the much-hated user space API is just a char
> device driver with 3 ioctls (that can be extended in future if need be) and
> the kernel API is acceptable to me. 

I think there is a little bit more to it than that.  It seems there is a new
ioctl for input/event devices to say "Any events queued here should be
treated as wake-up events".  There may be similar additions to other devices,
but I know of no details.

I wonder if we can get a complete statement of changes to the user-space
API...

>                                       Yes, there is some overlap between it
> and PM QoS, but IMhO that overlap may be reduced over time (eg. by
> using PM QoS requirements to implement suspend blockers). 
> 
> To me, the question boils down to whether or not we're able to persuade the
> Android people to use any other approach (eg. by demonstrating that something
> else is actually better), because even if we invent a brilliant new approach,
> but Android ends up using its old one anyway, the net result will be as though
> we haven't done anything useful.

Yes.  There is no point unless we can meet somewhere in the middle.  I think
that would have to include a full suspend that freezes all processes.
Solutions which reject that - while quite clever - would require too much
change to Android user-space to be acceptable.

NeilBrown

> 
> Rafael

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